diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index 28f9ac7f7de..c5e1ac28c9d 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -1761,7 +1761,7 @@ declare module 'vscode' {
 
 	//#region https://github.com/microsoft/vscode/issues/107467
 	// todo@API test or tests?
-	export namespace test {
+	export namespace tests {
 		/**
 		 * Creates a new test controller.
 		 *
@@ -1782,18 +1782,6 @@ declare module 'vscode' {
 		 * @stability experimental
 		 */
 		export function createTestObserver(): TestObserver;
-
-		/**
-		 * Creates a new managed {@link TestItem} instance. It can be added into
-		 * the {@link TestItem.children} of an existing item, or into the
-		 * {@link TestController.items}.
-		 * @param id Unique identifier for the TestItem.
-		 * @param label Human-readable label of the test item.
-		 * @param uri URI this TestItem is associated with. May be a file or directory.
-		 */
-		// todo@API move into TestController
-		export function createTestItem(id: string, label: string, uri?: Uri): TestItem;
-
 		/**
 		 * List of test results stored by the editor, sorted in descending
 		 * order by their `completedAt` time.
@@ -1851,13 +1839,10 @@ declare module 'vscode' {
 		readonly removed: ReadonlyArray<TestItem>;
 	}
 
-	// Todo@api: this is basically the same as the TaskGroup, which is a class that
-	// allows custom groups to be created. However I don't anticipate having any
-	// UI for that, so enum for now?
 	/**
-	 *
+	 * The kind of executions that {@link TestRunProfile | TestRunProfiles} control.
 	 */
-	export enum TestRunProfileGroup {
+	export enum TestRunProfileKind {
 		Run = 1,
 		Debug = 2,
 		Coverage = 3,
@@ -1879,16 +1864,16 @@ declare module 'vscode' {
 		label: string;
 
 		/**
-		 * Configures where this profile is grouped in the UI. If there
-		 * are no profiles for a group, it will not be available in the UI.
+		 * Configures what kind of execution this profile controls. If there
+		 * are no profiles for a kind, it will not be available in the UI.
 		 */
-		readonly group: TestRunProfileGroup;
+		readonly kind: TestRunProfileKind;
 
 		/**
 		 * Controls whether this profile is the default action that will
 		 * be taken when its group is actions. For example, if the user clicks
 		 * the generic "run all" button, then the default profile for
-		 * {@link TestRunProfileGroup.Run} will be executed.
+		 * {@link TestRunProfileKind.Run} will be executed.
 		 */
 		isDefault: boolean;
 
@@ -1928,9 +1913,9 @@ declare module 'vscode' {
 	 */
 	export interface TestController {
 		/**
-		 * The ID of the controller, passed in {@link vscode.test.createTestController}
+		 * The ID of the controller, passed in {@link vscode.tests.createTestController}.
+		 * This must be globally unique,
 		 */
-		// todo@api maybe explain what the id is used for and iff it must be globally unique or only unique within the extension
 		readonly id: string;
 
 		/**
@@ -1960,13 +1945,13 @@ declare module 'vscode' {
 		 * @param runHandler Function called to start a test run
 		 * @param isDefault Whether this is the default action for the group
 		 */
-		createRunProfile(label: string, group: TestRunProfileGroup, runHandler: (request: TestRunRequest, token: CancellationToken) => Thenable<void> | void, isDefault?: boolean): TestRunProfile;
+		createRunProfile(label: string, group: TestRunProfileKind, runHandler: (request: TestRunRequest, token: CancellationToken) => Thenable<void> | void, isDefault?: boolean): TestRunProfile;
 
 		/**
 		 * A function provided by the extension that the editor may call to request
 		 * children of a test item, if the {@link TestItem.canResolveChildren} is
 		 * `true`. When called, the item should discover children and call
-		 * {@link vscode.test.createTestItem} as children are discovered.
+		 * {@link vscode.tests.createTestItem} as children are discovered.
 		 *
 		 * The item in the explorer will automatically be marked as "busy" until
 		 * the function returns or the returned thenable resolves.
@@ -1984,7 +1969,7 @@ declare module 'vscode' {
 		 * {@link TestRunner} when a request is made to execute tests, and may also
 		 * be called if a test run is detected externally. Once created, tests
 		 * that are included in the results will be moved into the
-		 * {@link TestResultState.Pending} state. todo@API there is no Pending
+		 * {@link TestResultState.Queued} state.
 		 *
 		 * All runs created using the same `request` instance will be grouped
 		 * together. This is useful if, for example, a single suite of tests is
@@ -2001,6 +1986,17 @@ declare module 'vscode' {
 		 */
 		createTestRun(request: TestRunRequest, name?: string, persist?: boolean): TestRun;
 
+		/**
+		 * Creates a new managed {@link TestItem} instance. It can be added into
+		 * the {@link TestItem.children} of an existing item, or into the
+		 * {@link TestController.items}.
+		 * @param id Identifier for the TestItem. The test item's ID must be unique
+		 * in the {@link TestItemCollection} it's added to.
+		 * @param label Human-readable label of the test item.
+		 * @param uri URI this TestItem is associated with. May be a file or directory.
+		 */
+		createTestItem(id: string, label: string, uri?: Uri): TestItem;
+
 		/**
 		 * Unregisters the test controller, disposing of its associated tests
 		 * and unpersisted results.
@@ -2009,7 +2005,7 @@ declare module 'vscode' {
 	}
 
 	/**
-	 * Options given to {@link test.runTests}.
+	 * Options given to {@link tests.runTests}.
 	 */
 	export class TestRunRequest {
 		/**
@@ -2017,16 +2013,19 @@ declare module 'vscode' {
 		 * of the given tests and all children of the given tests, excluding
 		 * any tests that appear in {@link TestRunRequest.exclude}. If this is
 		 * not given, then the extension should simply run all tests.
+		 *
+		 * The process of running tests should resolve the children of any test
+		 * items who have not yet been resolved.
 		 */
-		// todo@API "...run all tests." which can mean resolve all tests first
 		include?: TestItem[];
 
 		/**
-		 * An array of tests the user has marked as excluded in the editor. May be
-		 * omitted if no exclusions were requested. Test controllers should not run
-		 * excluded tests or any children of excluded tests.
+		 * An array of tests the user has marked as excluded from the test included
+		 * in this run; exclusions should apply after inclusions.
+		 *
+		 * May be omitted if no exclusions were requested. Test controllers should
+		 * not run excluded tests or any children of excluded tests.
 		 */
-		// @todo@API say that exclude is more important than include!
 		exclude?: TestItem[];
 
 		/**
@@ -2047,7 +2046,6 @@ declare module 'vscode' {
 	/**
 	 * Options given to {@link TestController.runTests}
 	 */
-	// todo@API add readonly or rw `isPersisted: boolean`
 	export interface TestRun {
 		/**
 		 * The human-readable name of the run. This can be used to
@@ -2062,6 +2060,11 @@ declare module 'vscode' {
 		 */
 		readonly token: CancellationToken;
 
+		/**
+		 * Whether the test run will be persisteded across reloads by the editor UI.
+		 */
+		readonly isPersisted: boolean;
+
 		/**
 		 * Updates the state of the test in the run. Calling with method with nodes
 		 * outside the {@link TestRunRequest.tests} or in the {@link TestRunRequest.exclude}
@@ -2070,10 +2073,20 @@ declare module 'vscode' {
 		 *
 		 * @param test The test to update
 		 * @param state The state to assign to the test
+		 */
+		setState(test: TestItem, state: TestResultState): void;
+
+		/**
+		 * Updates the state of the test in the run. Calling with method with nodes
+		 * outside the {@link TestRunRequest.tests} or in the {@link TestRunRequest.exclude}
+		 * array will no-op. This override moves the test into a terminal state and
+		 * indicates how long it ran for.
+		 *
+		 * @param test The terminal test state
+		 * @param state The state to assign to the test
 		 * @param duration Optionally sets how long the test took to run, in milliseconds
 		 */
-		// todo@API clarify duration, either add doc or new composite type
-		setState(test: TestItem, state: TestResultState, duration?: number): void;
+		setState(test: TestItem, state: TestResultState.Passed | TestResultState.Failed | TestResultState.Errored, duration: number): void;
 
 		/**
 		 * Appends a message, such as an assertion error, to the test item.
@@ -2084,7 +2097,6 @@ declare module 'vscode' {
 		 * @param test The test to update
 		 * @param message The message to add
 		 */
-		// todo@API can this called many times, should this be part of setState?
 		appendMessage(test: TestItem, message: TestMessage): void;
 
 		/**
@@ -2098,8 +2110,7 @@ declare module 'vscode' {
 
 		/**
 		 * Signals that the end of the test run. Any tests included in the run whose
-		 * states have not been updated will be moved into
-		 * the {@link TestResultState.Unset} state.
+		 * states have not been updated will have their state reset.
 		 */
 		end(): void;
 	}
@@ -2110,13 +2121,10 @@ declare module 'vscode' {
 	 */
 	export interface TestItemCollection {
 		/**
-		 * Updates the items stored by the collection.
+		 * Replaces the items stored by the collection.
 		 * @param items Items to store, can be an array or other iterable.
 		 */
-		// todo@API better names: reset, update...
-		// todo@API no Iterable
-		// @ts-ignore
-		set(items: Iterable<TestItem>): void;
+		replace(items: readonly TestItem[]): void;
 
 		/**
 		 * Iterate over each entry in this collection.
@@ -2170,7 +2178,7 @@ declare module 'vscode' {
 		readonly children: TestItemCollection;
 
 		/**
-		 * The parent of this item, given in {@link vscode.test.createTestItem}.
+		 * The parent of this item, given in {@link vscode.tests.createTestItem}.
 		 * This is undefined top-level items in the `TestController` and for
 		 * items that aren't yet included in another item's {@link children}.
 		 */
@@ -2233,9 +2241,6 @@ declare module 'vscode' {
 	 * Possible states of tests in a test run.
 	 */
 	export enum TestResultState {
-		// Initial state
-		// todo@API what is this state for? not needed, has no references
-		Unset = 0,
 		// Test will be run, but is not currently running.
 		Queued = 1,
 		// Test is currently running
@@ -2249,17 +2254,6 @@ declare module 'vscode' {
 		// Test run failed for some other reason (compilation error, timeout, etc)
 		Errored = 6
 	}
-
-	/**
-	 * Represents the severity of test messages.
-	 */
-	export enum TestMessageSeverity {
-		Error = 0,
-		Warning = 1,
-		Information = 2,
-		Hint = 3
-	}
-
 	/**
 	 * Message associated with the test state. Can be linked to a specific
 	 * source range -- useful for assertion failures, for example.
@@ -2270,12 +2264,6 @@ declare module 'vscode' {
 		 */
 		message: string | MarkdownString;
 
-		/**
-		 * Message severity. Defaults to "Error".
-		 */
-		// todo@API maybe not needed? what does it change?
-		severity: TestMessageSeverity;
-
 		/**
 		 * Expected test output. If given with `actualOutput`, a diff view will be shown.
 		 */
@@ -2307,8 +2295,8 @@ declare module 'vscode' {
 	}
 
 	/**
-	 * TestResults can be provided to the editor in {@link test.publishTestResult},
-	 * or read from it in {@link test.testResults}.
+	 * TestResults can be provided to the editor in {@link tests.publishTestResult},
+	 * or read from it in {@link tests.testResults}.
 	 *
 	 * The results contain a 'snapshot' of the tests at the point when the test
 	 * run is complete. Therefore, information such as its {@link Range} may be
@@ -2328,7 +2316,7 @@ declare module 'vscode' {
 
 		/**
 		 * List of test results. The items in this array are the items that
-		 * were passed in the {@link test.runTests} method.
+		 * were passed in the {@link tests.runTests} method.
 		 */
 		results: ReadonlyArray<Readonly<TestResultSnapshot>>;
 	}
diff --git a/src/vs/workbench/api/browser/mainThreadTesting.ts b/src/vs/workbench/api/browser/mainThreadTesting.ts
index 74b6c20913b..efed1d862cb 100644
--- a/src/vs/workbench/api/browser/mainThreadTesting.ts
+++ b/src/vs/workbench/api/browser/mainThreadTesting.ts
@@ -10,9 +10,8 @@ import { isDefined } from 'vs/base/common/types';
 import { URI } from 'vs/base/common/uri';
 import { Range } from 'vs/editor/common/core/range';
 import { extHostNamedCustomer } from 'vs/workbench/api/common/extHostCustomers';
-import { TestResultState } from 'vs/workbench/api/common/extHostTypes';
 import { MutableObservableValue } from 'vs/workbench/contrib/testing/common/observableValue';
-import { ExtensionRunTestsRequest, ITestItem, ITestMessage, ITestRunProfile, ITestRunTask, ResolvedTestRunRequest, TestDiffOpType, TestsDiff } from 'vs/workbench/contrib/testing/common/testCollection';
+import { ExtensionRunTestsRequest, ITestItem, ITestMessage, ITestRunProfile, ITestRunTask, ResolvedTestRunRequest, TestDiffOpType, TestResultState, TestsDiff } from 'vs/workbench/contrib/testing/common/testCollection';
 import { ITestProfileService } from 'vs/workbench/contrib/testing/common/testConfigurationService';
 import { TestCoverage } from 'vs/workbench/contrib/testing/common/testCoverage';
 import { LiveTestResult } from 'vs/workbench/contrib/testing/common/testResult';
diff --git a/src/vs/workbench/api/common/extHost.api.impl.ts b/src/vs/workbench/api/common/extHost.api.impl.ts
index b2f9bbac361..9c2d5a17358 100644
--- a/src/vs/workbench/api/common/extHost.api.impl.ts
+++ b/src/vs/workbench/api/common/extHost.api.impl.ts
@@ -341,15 +341,11 @@ export function createApiFactoryAndRegisterActors(accessor: ServicesAccessor): I
 			? extHostTypes.ExtensionKind.Workspace
 			: extHostTypes.ExtensionKind.UI;
 
-		const test: typeof vscode.test = {
+		const tests: typeof vscode.tests = {
 			createTestController(provider, label) {
 				checkProposedApiEnabled(extension);
 				return extHostTesting.createTestController(provider, label);
 			},
-			createTestItem(id, label, uri) {
-				checkProposedApiEnabled(extension);
-				return extHostTesting.createTestItem(id, label, uri);
-			},
 			createTestObserver() {
 				checkProposedApiEnabled(extension);
 				return extHostTesting.createTestObserver();
@@ -1127,7 +1123,7 @@ export function createApiFactoryAndRegisterActors(accessor: ServicesAccessor): I
 			notebooks,
 			scm,
 			tasks,
-			test,
+			tests,
 			window,
 			workspace,
 			// types
@@ -1272,7 +1268,7 @@ export function createApiFactoryAndRegisterActors(accessor: ServicesAccessor): I
 			TestResultState: extHostTypes.TestResultState,
 			TestRunRequest: extHostTypes.TestRunRequest,
 			TestMessage: extHostTypes.TestMessage,
-			TestRunProfileGroup: extHostTypes.TestRunProfileGroup,
+			TestRunProfileKind: extHostTypes.TestRunProfileKind,
 			TextSearchCompleteMessageType: TextSearchCompleteMessageType,
 			TestMessageSeverity: extHostTypes.TestMessageSeverity,
 			CoveredCount: extHostTypes.CoveredCount,
diff --git a/src/vs/workbench/api/common/extHost.protocol.ts b/src/vs/workbench/api/common/extHost.protocol.ts
index 2478a77de03..1314b999a47 100644
--- a/src/vs/workbench/api/common/extHost.protocol.ts
+++ b/src/vs/workbench/api/common/extHost.protocol.ts
@@ -46,7 +46,7 @@ import { WorkspaceTrustRequestOptions } from 'vs/platform/workspace/common/works
 import { ExtensionActivationReason } from 'vs/workbench/api/common/extHostExtensionActivator';
 import { ExtHostInteractive } from 'vs/workbench/api/common/extHostInteractive';
 import { TunnelDto } from 'vs/workbench/api/common/extHostTunnelService';
-import { DebugConfigurationProviderTriggerKind, TestResultState } from 'vs/workbench/api/common/extHostTypes';
+import { DebugConfigurationProviderTriggerKind } from 'vs/workbench/api/common/extHostTypes';
 import { TreeDataTransferDTO } from 'vs/workbench/api/common/shared/treeDataTransfer';
 import * as tasks from 'vs/workbench/api/common/shared/tasks';
 import { SaveReason } from 'vs/workbench/common/editor';
@@ -58,7 +58,7 @@ import { ICellRange } from 'vs/workbench/contrib/notebook/common/notebookRange';
 import { InputValidationType } from 'vs/workbench/contrib/scm/common/scm';
 import { ITextQueryBuilderOptions } from 'vs/workbench/contrib/search/common/queryBuilder';
 import { ISerializableEnvironmentVariableCollection } from 'vs/workbench/contrib/terminal/common/environmentVariable';
-import { ExtensionRunTestsRequest, ISerializedTestResults, ITestItem, ITestMessage, ITestRunTask, RunTestForControllerRequest, ResolvedTestRunRequest, ITestIdWithSrc, TestsDiff, IFileCoverage, CoverageDetails, ITestRunProfile } from 'vs/workbench/contrib/testing/common/testCollection';
+import { ExtensionRunTestsRequest, ISerializedTestResults, ITestItem, ITestMessage, ITestRunTask, RunTestForControllerRequest, ResolvedTestRunRequest, ITestIdWithSrc, TestsDiff, IFileCoverage, CoverageDetails, ITestRunProfile, TestResultState } from 'vs/workbench/contrib/testing/common/testCollection';
 import { InternalTimelineOptions, Timeline, TimelineChangeEvent, TimelineOptions, TimelineProviderDescriptor } from 'vs/workbench/contrib/timeline/common/timeline';
 import { TypeHierarchyItem } from 'vs/workbench/contrib/typeHierarchy/common/typeHierarchy';
 import { EditorGroupColumn } from 'vs/workbench/services/editor/common/editorGroupColumn';
diff --git a/src/vs/workbench/api/common/extHostTesting.ts b/src/vs/workbench/api/common/extHostTesting.ts
index 7e67594dda6..3b52860190d 100644
--- a/src/vs/workbench/api/common/extHostTesting.ts
+++ b/src/vs/workbench/api/common/extHostTesting.ts
@@ -17,11 +17,11 @@ import { generateUuid } from 'vs/base/common/uuid';
 import { ExtHostTestingShape, MainContext, MainThreadTestingShape } from 'vs/workbench/api/common/extHost.protocol';
 import { ExtHostCommands } from 'vs/workbench/api/common/extHostCommands';
 import { IExtHostRpcService } from 'vs/workbench/api/common/extHostRpcService';
-import { TestItemImpl, TestItemRootImpl } from 'vs/workbench/api/common/extHostTestingPrivateApi';
+import { InvalidTestItemError, TestItemImpl, TestItemRootImpl } from 'vs/workbench/api/common/extHostTestingPrivateApi';
 import * as Convert from 'vs/workbench/api/common/extHostTypeConverters';
-import { TestRunProfileGroup, TestRunRequest } from 'vs/workbench/api/common/extHostTypes';
+import { TestRunProfileKind, TestRunRequest } from 'vs/workbench/api/common/extHostTypes';
 import { SingleUseTestCollection } from 'vs/workbench/contrib/testing/common/ownedTestCollection';
-import { AbstractIncrementalTestCollection, CoverageDetails, IFileCoverage, IncrementalChangeCollector, IncrementalTestCollectionItem, InternalTestItem, ISerializedTestResults, ITestIdWithSrc, ITestItem, RunTestForControllerRequest, TestRunProfileBitset, TestsDiff } from 'vs/workbench/contrib/testing/common/testCollection';
+import { AbstractIncrementalTestCollection, CoverageDetails, IFileCoverage, IncrementalChangeCollector, IncrementalTestCollectionItem, InternalTestItem, ISerializedTestResults, ITestIdWithSrc, ITestItem, RunTestForControllerRequest, TestResultState, TestRunProfileBitset, TestsDiff } from 'vs/workbench/contrib/testing/common/testCollection';
 import { TestId, TestIdPathParts, TestPosition } from 'vs/workbench/contrib/testing/common/testId';
 import type * as vscode from 'vscode';
 
@@ -86,6 +86,9 @@ export class ExtHostTesting implements ExtHostTestingShape {
 				profiles.set(profileId, profile);
 				return profile;
 			},
+			createTestItem(id, label, uri) {
+				return new TestItemImpl(controllerId, id, label, uri);
+			},
 			createTestRun: (request, name, persist = true) => {
 				return this.runTracker.createTestRun(controllerId, collection, request, name, persist);
 			},
@@ -115,13 +118,6 @@ export class ExtHostTesting implements ExtHostTestingShape {
 		return controller;
 	}
 
-	/**
-	 * Implements vscode.test.createTestItem
-	 */
-	public createTestItem(id: string, label: string, uri?: vscode.Uri) {
-		return new TestItemImpl(id, label, uri);
-	}
-
 	/**
 	 * Implements vscode.test.createTestObserver
 	 */
@@ -147,7 +143,7 @@ export class ExtHostTesting implements ExtHostTestingShape {
 		await this.proxy.$runTests({
 			targets: [{
 				testIds: req.include?.map(t => t.id) ?? [controller.collection.root.id],
-				profileGroup: profileGroupToBitset[profile.group],
+				profileGroup: profileGroupToBitset[profile.kind],
 				profileId: profile.profileId,
 				controllerId: profile.controllerId,
 			}],
@@ -396,11 +392,11 @@ export class TestRunCoordinator {
 
 		// If there is not an existing tracked extension for the request, start
 		// a new, detached session.
-		const dto = TestRunDto.fromPublic(controllerId, collection, request);
+		const dto = TestRunDto.fromPublic(controllerId, collection, request, persist);
 		const profile = tryGetProfileFromTestRunReq(request);
 		this.proxy.$startedExtensionTestRun({
 			controllerId,
-			profile: profile && { group: profileGroupToBitset[profile.group], id: profile.profileId },
+			profile: profile && { group: profileGroupToBitset[profile.kind], id: profile.profileId },
 			exclude: request.exclude?.map(t => t.id) ?? [],
 			id: dto.id,
 			include: request.include?.map(t => t.id) ?? [collection.root.id],
@@ -436,12 +432,13 @@ export class TestRunDto {
 	private readonly includePrefix: string[];
 	private readonly excludePrefix: string[];
 
-	public static fromPublic(controllerId: string, collection: SingleUseTestCollection, request: vscode.TestRunRequest) {
+	public static fromPublic(controllerId: string, collection: SingleUseTestCollection, request: vscode.TestRunRequest, persist: boolean) {
 		return new TestRunDto(
 			controllerId,
 			generateUuid(),
 			request.include?.map(t => TestId.fromExtHostTestItem(t, controllerId).toString()) ?? [controllerId],
 			request.exclude?.map(t => TestId.fromExtHostTestItem(t, controllerId).toString()) ?? [],
+			persist,
 			collection,
 		);
 	}
@@ -452,6 +449,7 @@ export class TestRunDto {
 			request.runId,
 			request.testIds,
 			request.excludeExtIds,
+			true,
 			collection,
 		);
 	}
@@ -461,6 +459,7 @@ export class TestRunDto {
 		public readonly id: string,
 		include: string[],
 		exclude: string[],
+		public readonly isPersisted: boolean,
 		public readonly colllection: SingleUseTestCollection,
 	) {
 		this.includePrefix = include.map(id => id + TestIdPathParts.Delimiter);
@@ -562,6 +561,10 @@ class TestRunImpl implements vscode.TestRun {
 		return this.#coverage.coverageProvider;
 	}
 
+	public get isPersisted() {
+		return this.#req.isPersisted;
+	}
+
 	constructor(
 		public readonly name: string | undefined,
 		public readonly token: CancellationToken,
@@ -584,7 +587,7 @@ class TestRunImpl implements vscode.TestRun {
 		const req = this.#req;
 		if (!this.#ended && req.isIncluded(test)) {
 			this.ensureTestIsKnown(test);
-			this.#proxy.$updateTestStateInRun(req.id, this.taskId, TestId.fromExtHostTestItem(test, req.controllerId).toString(), state, duration);
+			this.#proxy.$updateTestStateInRun(req.id, this.taskId, TestId.fromExtHostTestItem(test, req.controllerId).toString(), state as number as TestResultState, duration);
 		}
 	}
 
@@ -611,15 +614,18 @@ class TestRunImpl implements vscode.TestRun {
 	}
 
 	private ensureTestIsKnown(test: vscode.TestItem) {
+		if (!(test instanceof TestItemImpl)) {
+			throw new InvalidTestItemError(test.id);
+		}
+
 		const sent = this.#sharedIds;
 		if (sent.has(test.id)) {
 			return;
 		}
 
 		const chain: ITestItem[] = [];
-		const root = this.#req.colllection.root;
 		while (true) {
-			chain.unshift(Convert.TestItem.from(test, root.id));
+			chain.unshift(Convert.TestItem.from(test as TestItemImpl));
 
 			if (sent.has(test.id)) {
 				break;
@@ -633,9 +639,10 @@ class TestRunImpl implements vscode.TestRun {
 			test = test.parent;
 		}
 
+		const root = this.#req.colllection.root;
 		if (!sent.has(root.id)) {
 			sent.add(root.id);
-			chain.unshift(Convert.TestItem.from(root, root.id));
+			chain.unshift(Convert.TestItem.from(root));
 		}
 
 		this.#proxy.$addTestsToRun(this.#req.controllerId, this.#req.id, chain);
@@ -867,15 +874,15 @@ export class TestRunProfileImpl implements vscode.TestRunProfile {
 		public readonly controllerId: string,
 		public readonly profileId: number,
 		private _label: string,
-		public readonly group: vscode.TestRunProfileGroup,
+		public readonly kind: vscode.TestRunProfileKind,
 		public runHandler: (request: vscode.TestRunRequest, token: vscode.CancellationToken) => Thenable<void> | void,
 		private _isDefault = false,
 	) {
 		this.#proxy = proxy;
 
-		const groupBitset = profileGroupToBitset[group];
+		const groupBitset = profileGroupToBitset[kind];
 		if (typeof groupBitset !== 'number') {
-			throw new Error(`Unknown TestRunProfile.group ${group}`);
+			throw new Error(`Unknown TestRunProfile.group ${kind}`);
 		}
 
 		this.#proxy.$publishTestRunProfile({
@@ -893,8 +900,8 @@ export class TestRunProfileImpl implements vscode.TestRunProfile {
 	}
 }
 
-const profileGroupToBitset: { [K in TestRunProfileGroup]: TestRunProfileBitset } = {
-	[TestRunProfileGroup.Coverage]: TestRunProfileBitset.Coverage,
-	[TestRunProfileGroup.Debug]: TestRunProfileBitset.Debug,
-	[TestRunProfileGroup.Run]: TestRunProfileBitset.Run,
+const profileGroupToBitset: { [K in TestRunProfileKind]: TestRunProfileBitset } = {
+	[TestRunProfileKind.Coverage]: TestRunProfileBitset.Coverage,
+	[TestRunProfileKind.Debug]: TestRunProfileBitset.Debug,
+	[TestRunProfileKind.Run]: TestRunProfileBitset.Run,
 };
diff --git a/src/vs/workbench/api/common/extHostTestingPrivateApi.ts b/src/vs/workbench/api/common/extHostTestingPrivateApi.ts
index 9c7a10a1bc4..2f6c84e9f0b 100644
--- a/src/vs/workbench/api/common/extHostTestingPrivateApi.ts
+++ b/src/vs/workbench/api/common/extHostTestingPrivateApi.ts
@@ -46,26 +46,25 @@ export type ExtHostTestItemEvent =
 	| ITestItemBulkReplace;
 
 export interface IExtHostTestItemApi {
+	controllerId: string;
 	parent?: TestItemImpl;
 	listener?: (evt: ExtHostTestItemEvent) => void;
 }
 
 const eventPrivateApis = new WeakMap<TestItemImpl, IExtHostTestItemApi>();
 
+export const createPrivateApiFor = (impl: TestItemImpl, controllerId: string) => {
+	const api: IExtHostTestItemApi = { controllerId };
+	eventPrivateApis.set(impl, api);
+	return api;
+};
+
 /**
  * Gets the private API for a test item implementation. This implementation
  * is a managed object, but we keep a weakmap to avoid exposing any of the
  * internals to extensions.
  */
-export const getPrivateApiFor = (impl: TestItemImpl) => {
-	let api = eventPrivateApis.get(impl);
-	if (!api) {
-		api = {};
-		eventPrivateApis.set(impl, api);
-	}
-
-	return api;
-};
+export const getPrivateApiFor = (impl: TestItemImpl) => eventPrivateApis.get(impl)!;
 
 const testItemPropAccessor = <K extends keyof vscode.TestItem>(
 	api: IExtHostTestItemApi,
@@ -145,9 +144,16 @@ export class InvalidTestItemError extends Error {
 	}
 }
 
+export class MixedTestItemController extends Error {
+	constructor(id: string, ctrlA: string, ctrlB: string) {
+		super(`TestItem with ID "${id}" is from controller "${ctrlA}" and cannot be added as a child of an item from controller "${ctrlB}".`);
+	}
+}
+
+
 export type TestItemCollectionImpl = vscode.TestItemCollection & { toJSON(): readonly TestItemImpl[] } & Iterable<TestItemImpl>;
 
-export const createTestItemCollection = (owningItem: TestItemImpl): TestItemCollectionImpl => {
+const createTestItemCollection = (owningItem: TestItemImpl): TestItemCollectionImpl => {
 	const api = getPrivateApiFor(owningItem);
 	let mapped = new Map<string, TestItemImpl>();
 
@@ -160,7 +166,7 @@ export const createTestItemCollection = (owningItem: TestItemImpl): TestItemColl
 		},
 
 		/** @inheritdoc */
-		set(items: Iterable<vscode.TestItem>) {
+		replace(items: Iterable<vscode.TestItem>) {
 			const newMapped = new Map<string, TestItemImpl>();
 			const toDelete = new Set(mapped.keys());
 			const bulk: ITestItemBulkReplace = { op: ExtHostTestItemEventOp.Bulk, ops: [] };
@@ -170,6 +176,11 @@ export const createTestItemCollection = (owningItem: TestItemImpl): TestItemColl
 					throw new InvalidTestItemError(item.id);
 				}
 
+				const itemController = getPrivateApiFor(item).controllerId;
+				if (itemController !== api.controllerId) {
+					throw new MixedTestItemController(item.id, itemController, api.controllerId);
+				}
+
 				if (newMapped.has(item.id)) {
 					throw new DuplicateTestItemError(item.id);
 				}
@@ -241,12 +252,12 @@ export class TestItemImpl implements vscode.TestItem {
 	/**
 	 * Note that data is deprecated and here for back-compat only
 	 */
-	constructor(id: string, label: string, uri: vscode.Uri | undefined) {
-		const api = getPrivateApiFor(this);
+	constructor(controllerId: string, id: string, label: string, uri: vscode.Uri | undefined) {
 		if (id.includes(TestIdPathParts.Delimiter)) {
 			throw new Error(`Test IDs may not include the ${JSON.stringify(id)} symbol`);
 		}
 
+		const api = createPrivateApiFor(this, controllerId);
 		Object.defineProperties(this, {
 			id: {
 				value: id,
@@ -281,6 +292,6 @@ export class TestItemImpl implements vscode.TestItem {
 
 export class TestItemRootImpl extends TestItemImpl {
 	constructor(controllerId: string, label: string) {
-		super(controllerId, label, undefined);
+		super(controllerId, controllerId, label, undefined);
 	}
 }
diff --git a/src/vs/workbench/api/common/extHostTypeConverters.ts b/src/vs/workbench/api/common/extHostTypeConverters.ts
index 769a05510ad..91f265f21ad 100644
--- a/src/vs/workbench/api/common/extHostTypeConverters.ts
+++ b/src/vs/workbench/api/common/extHostTypeConverters.ts
@@ -1642,7 +1642,7 @@ export namespace TestMessage {
 	export function from(message: vscode.TestMessage): ITestMessage {
 		return {
 			message: MarkdownString.fromStrict(message.message) || '',
-			severity: message.severity,
+			severity: types.TestMessageSeverity.Error,
 			expectedOutput: message.expectedOutput,
 			actualOutput: message.actualOutput,
 			location: message.location ? location.from(message.location) as any : undefined,
@@ -1651,7 +1651,6 @@ export namespace TestMessage {
 
 	export function to(item: ITestMessage): vscode.TestMessage {
 		const message = new types.TestMessage(typeof item.message === 'string' ? item.message : MarkdownString.to(item.message));
-		message.severity = item.severity;
 		message.actualOutput = item.actualOutput;
 		message.expectedOutput = item.expectedOutput;
 		return message;
@@ -1661,9 +1660,9 @@ export namespace TestMessage {
 export namespace TestItem {
 	export type Raw = vscode.TestItem;
 
-	export function from(item: vscode.TestItem, controllerId: string): ITestItem {
+	export function from(item: TestItemImpl): ITestItem {
 		return {
-			extId: TestId.fromExtHostTestItem(item, controllerId).toString(),
+			extId: TestId.fromExtHostTestItem(item, getPrivateApiFor(item).controllerId).toString(),
 			label: item.label,
 			uri: item.uri,
 			range: Range.from(item.range) || null,
@@ -1686,7 +1685,8 @@ export namespace TestItem {
 	}
 
 	function to(item: ITestItem): TestItemImpl {
-		const testItem = new TestItemImpl(TestId.fromString(item.extId).localId, item.label, URI.revive(item.uri));
+		const testId = TestId.fromString(item.extId);
+		const testItem = new TestItemImpl(testId.controllerId, testId.localId, item.label, URI.revive(item.uri));
 		testItem.range = Range.to(item.range || undefined);
 		testItem.description = item.description || undefined;
 		return testItem;
@@ -1710,7 +1710,7 @@ export namespace TestResults {
 			...TestItem.toPlain(item.item),
 			parent: undefined,
 			taskStates: item.tasks.map(t => ({
-				state: t.state,
+				state: t.state as number as types.TestResultState,
 				duration: t.duration,
 				messages: t.messages.map(TestMessage.to),
 			})),
diff --git a/src/vs/workbench/api/common/extHostTypes.ts b/src/vs/workbench/api/common/extHostTypes.ts
index fc676d84adc..54b63602bc1 100644
--- a/src/vs/workbench/api/common/extHostTypes.ts
+++ b/src/vs/workbench/api/common/extHostTypes.ts
@@ -3286,7 +3286,6 @@ export class PortAttributes {
 
 //#region Testing
 export enum TestResultState {
-	Unset = 0,
 	Queued = 1,
 	Running = 2,
 	Passed = 3,
@@ -3302,7 +3301,7 @@ export enum TestMessageSeverity {
 	Hint = 3
 }
 
-export enum TestRunProfileGroup {
+export enum TestRunProfileKind {
 	Run = 1,
 	Debug = 2,
 	Coverage = 3,
@@ -3319,7 +3318,6 @@ export class TestRunRequest implements vscode.TestRunRequest {
 
 @es5ClassCompat
 export class TestMessage implements vscode.TestMessage {
-	public severity = TestMessageSeverity.Error;
 	public expectedOutput?: string;
 	public actualOutput?: string;
 
diff --git a/src/vs/workbench/contrib/testing/browser/explorerProjections/hierarchalByLocation.ts b/src/vs/workbench/contrib/testing/browser/explorerProjections/hierarchalByLocation.ts
index 0816013c65c..7587d96b5e0 100644
--- a/src/vs/workbench/contrib/testing/browser/explorerProjections/hierarchalByLocation.ts
+++ b/src/vs/workbench/contrib/testing/browser/explorerProjections/hierarchalByLocation.ts
@@ -9,12 +9,11 @@ import { FuzzyScore } from 'vs/base/common/filters';
 import { Iterable } from 'vs/base/common/iterator';
 import { Disposable } from 'vs/base/common/lifecycle';
 import { isDefined } from 'vs/base/common/types';
-import { TestResultState } from 'vs/workbench/api/common/extHostTypes';
 import { ByLocationTestItemElement } from 'vs/workbench/contrib/testing/browser/explorerProjections/hierarchalNodes';
 import { IActionableTestTreeElement, ITestTreeProjection, TestExplorerTreeElement, TestItemTreeElement, TestTreeErrorMessage } from 'vs/workbench/contrib/testing/browser/explorerProjections/index';
 import { NodeChangeList, NodeRenderDirective, NodeRenderFn, peersHaveChildren } from 'vs/workbench/contrib/testing/browser/explorerProjections/nodeHelper';
 import { IComputedStateAndDurationAccessor, refreshComputedState } from 'vs/workbench/contrib/testing/common/getComputedState';
-import { InternalTestItem, TestDiffOpType, TestItemExpandState, TestsDiff } from 'vs/workbench/contrib/testing/common/testCollection';
+import { InternalTestItem, TestDiffOpType, TestItemExpandState, TestResultState, TestsDiff } from 'vs/workbench/contrib/testing/common/testCollection';
 import { ITestResultService } from 'vs/workbench/contrib/testing/common/testResultService';
 import { ITestService } from 'vs/workbench/contrib/testing/common/testService';
 
diff --git a/src/vs/workbench/contrib/testing/browser/explorerProjections/index.ts b/src/vs/workbench/contrib/testing/browser/explorerProjections/index.ts
index 77c47e7e6f6..de6f154b00c 100644
--- a/src/vs/workbench/contrib/testing/browser/explorerProjections/index.ts
+++ b/src/vs/workbench/contrib/testing/browser/explorerProjections/index.ts
@@ -10,8 +10,7 @@ import { IMarkdownString } from 'vs/base/common/htmlContent';
 import { Iterable } from 'vs/base/common/iterator';
 import { IDisposable } from 'vs/base/common/lifecycle';
 import { MarshalledId } from 'vs/base/common/marshalling';
-import { TestResultState } from 'vs/workbench/api/common/extHostTypes';
-import { identifyTest, InternalTestItem, ITestIdWithSrc, ITestItemContext } from 'vs/workbench/contrib/testing/common/testCollection';
+import { TestResultState, identifyTest, InternalTestItem, ITestIdWithSrc, ITestItemContext } from 'vs/workbench/contrib/testing/common/testCollection';
 
 /**
  * Describes a rendering of tests in the explorer view. Different
diff --git a/src/vs/workbench/contrib/testing/browser/icons.ts b/src/vs/workbench/contrib/testing/browser/icons.ts
index 0d41f755b26..6e393e106d2 100644
--- a/src/vs/workbench/contrib/testing/browser/icons.ts
+++ b/src/vs/workbench/contrib/testing/browser/icons.ts
@@ -7,8 +7,9 @@ import { Codicon } from 'vs/base/common/codicons';
 import { localize } from 'vs/nls';
 import { registerIcon } from 'vs/platform/theme/common/iconRegistry';
 import { registerThemingParticipant, ThemeIcon } from 'vs/platform/theme/common/themeService';
-import { TestMessageSeverity, TestResultState } from 'vs/workbench/api/common/extHostTypes';
+import { TestMessageSeverity } from 'vs/workbench/api/common/extHostTypes';
 import { testingColorRunAction, testMessageSeverityColors, testStatesToIconColors } from 'vs/workbench/contrib/testing/browser/theme';
+import { TestResultState } from 'vs/workbench/contrib/testing/common/testCollection';
 
 export const testingViewIcon = registerIcon('test-view-icon', Codicon.beaker, localize('testViewIcon', 'View icon of the test view.'));
 export const testingRunIcon = registerIcon('testing-run-icon', Codicon.run, localize('testingRunIcon', 'Icon of the "run test" action.'));
diff --git a/src/vs/workbench/contrib/testing/browser/testingDecorations.ts b/src/vs/workbench/contrib/testing/browser/testingDecorations.ts
index 4e844b4539c..d8cf9648c70 100644
--- a/src/vs/workbench/contrib/testing/browser/testingDecorations.ts
+++ b/src/vs/workbench/contrib/testing/browser/testingDecorations.ts
@@ -23,14 +23,14 @@ import { IConfigurationService } from 'vs/platform/configuration/common/configur
 import { IContextMenuService } from 'vs/platform/contextview/browser/contextView';
 import { IInstantiationService } from 'vs/platform/instantiation/common/instantiation';
 import { IThemeService, themeColorFromId, ThemeIcon } from 'vs/platform/theme/common/themeService';
-import { TestMessageSeverity, TestResultState } from 'vs/workbench/api/common/extHostTypes';
+import { TestMessageSeverity } from 'vs/workbench/api/common/extHostTypes';
 import { BREAKPOINT_EDITOR_CONTRIBUTION_ID, IBreakpointEditorContribution } from 'vs/workbench/contrib/debug/common/debug';
 import { testingRunAllIcon, testingRunIcon, testingStatesToIcons } from 'vs/workbench/contrib/testing/browser/icons';
 import { TestingOutputPeekController } from 'vs/workbench/contrib/testing/browser/testingOutputPeek';
 import { testMessageSeverityColors } from 'vs/workbench/contrib/testing/browser/theme';
 import { DefaultGutterClickAction, getTestingConfiguration, TestingConfigKeys } from 'vs/workbench/contrib/testing/common/configuration';
 import { labelForTestInState } from 'vs/workbench/contrib/testing/common/constants';
-import { identifyTest, IncrementalTestCollectionItem, InternalTestItem, IRichLocation, ITestMessage, ITestRunProfile, TestResultItem, TestRunProfileBitset } from 'vs/workbench/contrib/testing/common/testCollection';
+import { identifyTest, IncrementalTestCollectionItem, InternalTestItem, IRichLocation, ITestMessage, ITestRunProfile, TestResultItem, TestResultState, TestRunProfileBitset } from 'vs/workbench/contrib/testing/common/testCollection';
 import { ITestProfileService } from 'vs/workbench/contrib/testing/common/testConfigurationService';
 import { maxPriority } from 'vs/workbench/contrib/testing/common/testingStates';
 import { buildTestUri, TestUriType } from 'vs/workbench/contrib/testing/common/testingUri';
diff --git a/src/vs/workbench/contrib/testing/browser/testingExplorerView.ts b/src/vs/workbench/contrib/testing/browser/testingExplorerView.ts
index 0fb264b1f7f..ac81f5f7734 100644
--- a/src/vs/workbench/contrib/testing/browser/testingExplorerView.ts
+++ b/src/vs/workbench/contrib/testing/browser/testingExplorerView.ts
@@ -43,7 +43,6 @@ import { ITelemetryService } from 'vs/platform/telemetry/common/telemetry';
 import { foreground } from 'vs/platform/theme/common/colorRegistry';
 import { attachButtonStyler } from 'vs/platform/theme/common/styler';
 import { IThemeService, registerThemingParticipant, ThemeIcon } from 'vs/platform/theme/common/themeService';
-import { TestResultState } from 'vs/workbench/api/common/extHostTypes';
 import { IResourceLabel, IResourceLabelOptions, IResourceLabelProps, ResourceLabels } from 'vs/workbench/browser/labels';
 import { ViewPane } from 'vs/workbench/browser/parts/views/viewPane';
 import { IViewletViewOptions } from 'vs/workbench/browser/parts/views/viewsViewlet';
@@ -57,7 +56,7 @@ import { ITestExplorerFilterState, TestExplorerFilterState, TestingExplorerFilte
 import { ITestingProgressUiService } from 'vs/workbench/contrib/testing/browser/testingProgressUiService';
 import { getTestingConfiguration, TestingConfigKeys } from 'vs/workbench/contrib/testing/common/configuration';
 import { labelForTestInState, TestExplorerStateFilter, TestExplorerViewMode, TestExplorerViewSorting, Testing, testStateNames } from 'vs/workbench/contrib/testing/common/constants';
-import { identifyTest, ITestRunProfile, TestItemExpandState, TestRunProfileBitset } from 'vs/workbench/contrib/testing/common/testCollection';
+import { identifyTest, ITestRunProfile, TestItemExpandState, TestResultState, TestRunProfileBitset } from 'vs/workbench/contrib/testing/common/testCollection';
 import { ITestProfileService } from 'vs/workbench/contrib/testing/common/testConfigurationService';
 import { TestId } from 'vs/workbench/contrib/testing/common/testId';
 import { TestingContextKeys } from 'vs/workbench/contrib/testing/common/testingContextKeys';
diff --git a/src/vs/workbench/contrib/testing/browser/testingOutputPeek.ts b/src/vs/workbench/contrib/testing/browser/testingOutputPeek.ts
index 5337fc08f7c..a2455fd1101 100644
--- a/src/vs/workbench/contrib/testing/browser/testingOutputPeek.ts
+++ b/src/vs/workbench/contrib/testing/browser/testingOutputPeek.ts
@@ -49,7 +49,6 @@ import { KeybindingWeight } from 'vs/platform/keybinding/common/keybindingsRegis
 import { WorkbenchCompressibleObjectTree } from 'vs/platform/list/browser/listService';
 import { textLinkActiveForeground, textLinkForeground } from 'vs/platform/theme/common/colorRegistry';
 import { IColorTheme, IThemeService, registerThemingParticipant, ThemeIcon } from 'vs/platform/theme/common/themeService';
-import { TestResultState } from 'vs/workbench/api/common/extHostTypes';
 import { IResourceLabel, ResourceLabels } from 'vs/workbench/browser/labels';
 import { EditorModel } from 'vs/workbench/common/editor/editorModel';
 import { flatTestItemDelimiter } from 'vs/workbench/contrib/testing/browser/explorerProjections/display';
@@ -59,7 +58,7 @@ import { ITestingOutputTerminalService } from 'vs/workbench/contrib/testing/brow
 import { testingPeekBorder } from 'vs/workbench/contrib/testing/browser/theme';
 import { AutoOpenPeekViewWhen, getTestingConfiguration, TestingConfigKeys } from 'vs/workbench/contrib/testing/common/configuration';
 import { Testing } from 'vs/workbench/contrib/testing/common/constants';
-import { IRichLocation, ITestItem, ITestMessage, ITestRunTask, ITestTaskState, TestResultItem, TestRunProfileBitset } from 'vs/workbench/contrib/testing/common/testCollection';
+import { IRichLocation, ITestItem, ITestMessage, ITestRunTask, ITestTaskState, TestResultItem, TestResultState, TestRunProfileBitset } from 'vs/workbench/contrib/testing/common/testCollection';
 import { ITestProfileService } from 'vs/workbench/contrib/testing/common/testConfigurationService';
 import { TestingContextKeys } from 'vs/workbench/contrib/testing/common/testingContextKeys';
 import { ITestingPeekOpener } from 'vs/workbench/contrib/testing/common/testingPeekOpener';
diff --git a/src/vs/workbench/contrib/testing/browser/theme.ts b/src/vs/workbench/contrib/testing/browser/theme.ts
index a164b31b96a..d942dd4516a 100644
--- a/src/vs/workbench/contrib/testing/browser/theme.ts
+++ b/src/vs/workbench/contrib/testing/browser/theme.ts
@@ -7,8 +7,9 @@ import { Color, RGBA } from 'vs/base/common/color';
 import { localize } from 'vs/nls';
 import { editorErrorForeground, editorForeground, editorHintForeground, editorInfoForeground, editorWarningForeground, inputActiveOptionBackground, inputActiveOptionBorder, inputActiveOptionForeground, registerColor } from 'vs/platform/theme/common/colorRegistry';
 import { registerThemingParticipant } from 'vs/platform/theme/common/themeService';
-import { TestMessageSeverity, TestResultState } from 'vs/workbench/api/common/extHostTypes';
+import { TestMessageSeverity } from 'vs/workbench/api/common/extHostTypes';
 import { ACTIVITY_BAR_BADGE_BACKGROUND } from 'vs/workbench/common/theme';
+import { TestResultState } from 'vs/workbench/contrib/testing/common/testCollection';
 
 export const testingColorIconFailed = registerColor('testing.iconFailed', {
 	dark: '#f14c4c',
diff --git a/src/vs/workbench/contrib/testing/common/constants.ts b/src/vs/workbench/contrib/testing/common/constants.ts
index a3b12660609..8378f860fed 100644
--- a/src/vs/workbench/contrib/testing/common/constants.ts
+++ b/src/vs/workbench/contrib/testing/common/constants.ts
@@ -4,8 +4,7 @@
  *--------------------------------------------------------------------------------------------*/
 
 import { localize } from 'vs/nls';
-import { TestResultState } from 'vs/workbench/api/common/extHostTypes';
-import { TestRunProfileBitset } from 'vs/workbench/contrib/testing/common/testCollection';
+import { TestResultState, TestRunProfileBitset } from 'vs/workbench/contrib/testing/common/testCollection';
 
 export const enum Testing {
 	// marked as "extension" so that any existing test extensions are assigned to it.
diff --git a/src/vs/workbench/contrib/testing/common/getComputedState.ts b/src/vs/workbench/contrib/testing/common/getComputedState.ts
index c26b076d736..2599c32d270 100644
--- a/src/vs/workbench/contrib/testing/common/getComputedState.ts
+++ b/src/vs/workbench/contrib/testing/common/getComputedState.ts
@@ -4,7 +4,7 @@
  *--------------------------------------------------------------------------------------------*/
 
 import { Iterable } from 'vs/base/common/iterator';
-import { TestResultState } from 'vs/workbench/api/common/extHostTypes';
+import { TestResultState } from 'vs/workbench/contrib/testing/common/testCollection';
 import { maxPriority, statePriority } from 'vs/workbench/contrib/testing/common/testingStates';
 
 /**
diff --git a/src/vs/workbench/contrib/testing/common/ownedTestCollection.ts b/src/vs/workbench/contrib/testing/common/ownedTestCollection.ts
index b6c4494f239..f09e4163c94 100644
--- a/src/vs/workbench/contrib/testing/common/ownedTestCollection.ts
+++ b/src/vs/workbench/contrib/testing/common/ownedTestCollection.ts
@@ -218,7 +218,7 @@ export class SingleUseTestCollection extends Disposable {
 					parent: internal.parent && internal.parent.toString(),
 					controllerId: this.controllerId,
 					expand: internal.expand,
-					item: Convert.TestItem.from(actual, this.root.id),
+					item: Convert.TestItem.from(actual),
 				},
 			]);
 
diff --git a/src/vs/workbench/contrib/testing/common/testCollection.ts b/src/vs/workbench/contrib/testing/common/testCollection.ts
index 4df2dbaf31e..82da7da4fa0 100644
--- a/src/vs/workbench/contrib/testing/common/testCollection.ts
+++ b/src/vs/workbench/contrib/testing/common/testCollection.ts
@@ -8,15 +8,23 @@ import { MarshalledId } from 'vs/base/common/marshalling';
 import { URI } from 'vs/base/common/uri';
 import { IPosition } from 'vs/editor/common/core/position';
 import { IRange, Range } from 'vs/editor/common/core/range';
-import { TestMessageSeverity, TestResultState } from 'vs/workbench/api/common/extHostTypes';
-
-export { TestResultState } from 'vs/workbench/api/common/extHostTypes';
+import { TestMessageSeverity } from 'vs/workbench/api/common/extHostTypes';
 
 export interface ITestIdWithSrc {
 	testId: string;
 	controllerId: string;
 }
 
+export const enum TestResultState {
+	Unset = 0,
+	Queued = 1,
+	Running = 2,
+	Passed = 3,
+	Failed = 4,
+	Skipped = 5,
+	Errored = 6
+}
+
 export const identifyTest = (test: { controllerId: string, item: { extId: string } }): ITestIdWithSrc =>
 	({ testId: test.item.extId, controllerId: test.controllerId });
 
@@ -98,6 +106,7 @@ export interface IRichLocation {
 
 export interface ITestMessage {
 	message: string | IMarkdownString;
+	/** @deprecated */
 	severity: TestMessageSeverity;
 	expectedOutput: string | undefined;
 	actualOutput: string | undefined;
diff --git a/src/vs/workbench/contrib/testing/common/testId.ts b/src/vs/workbench/contrib/testing/common/testId.ts
index 1fe4d2f7b35..3540bdc80ae 100644
--- a/src/vs/workbench/contrib/testing/common/testId.ts
+++ b/src/vs/workbench/contrib/testing/common/testId.ts
@@ -92,6 +92,13 @@ export class TestId {
 		return this.path[this.viewEnd - 1];
 	}
 
+	/**
+	 * Gets whether this ID refers to the root.
+	 */
+	public get controllerId() {
+		return this.path[0];
+	}
+
 	/**
 	 * Gets whether this ID refers to the root.
 	 */
diff --git a/src/vs/workbench/contrib/testing/common/testResult.ts b/src/vs/workbench/contrib/testing/common/testResult.ts
index 0c050e17ce3..2dc4b7223d9 100644
--- a/src/vs/workbench/contrib/testing/common/testResult.ts
+++ b/src/vs/workbench/contrib/testing/common/testResult.ts
@@ -10,10 +10,9 @@ import { DisposableStore } from 'vs/base/common/lifecycle';
 import { URI } from 'vs/base/common/uri';
 import { Range } from 'vs/editor/common/core/range';
 import { localize } from 'vs/nls';
-import { TestResultState } from 'vs/workbench/api/common/extHostTypes';
 import { IComputedStateAccessor, refreshComputedState } from 'vs/workbench/contrib/testing/common/getComputedState';
 import { IObservableValue, MutableObservableValue, staticObservableValue } from 'vs/workbench/contrib/testing/common/observableValue';
-import { ISerializedTestResults, ITestItem, ITestMessage, ITestRunTask, ITestTaskState, ResolvedTestRunRequest, TestItemExpandState, TestResultItem } from 'vs/workbench/contrib/testing/common/testCollection';
+import { ISerializedTestResults, ITestItem, ITestMessage, ITestRunTask, ITestTaskState, ResolvedTestRunRequest, TestItemExpandState, TestResultItem, TestResultState } from 'vs/workbench/contrib/testing/common/testCollection';
 import { TestCoverage } from 'vs/workbench/contrib/testing/common/testCoverage';
 import { maxPriority, statesInOrder } from 'vs/workbench/contrib/testing/common/testingStates';
 
diff --git a/src/vs/workbench/contrib/testing/common/testResultService.ts b/src/vs/workbench/contrib/testing/common/testResultService.ts
index 251037e39d8..30cee650e40 100644
--- a/src/vs/workbench/contrib/testing/common/testResultService.ts
+++ b/src/vs/workbench/contrib/testing/common/testResultService.ts
@@ -10,8 +10,7 @@ import { once } from 'vs/base/common/functional';
 import { generateUuid } from 'vs/base/common/uuid';
 import { IContextKey, IContextKeyService } from 'vs/platform/contextkey/common/contextkey';
 import { createDecorator } from 'vs/platform/instantiation/common/instantiation';
-import { TestResultState } from 'vs/workbench/api/common/extHostTypes';
-import { ExtensionRunTestsRequest, ITestRunProfile, ResolvedTestRunRequest, TestResultItem, TestRunProfileBitset } from 'vs/workbench/contrib/testing/common/testCollection';
+import { ExtensionRunTestsRequest, ITestRunProfile, ResolvedTestRunRequest, TestResultItem, TestResultState, TestRunProfileBitset } from 'vs/workbench/contrib/testing/common/testCollection';
 import { ITestProfileService } from 'vs/workbench/contrib/testing/common/testConfigurationService';
 import { TestingContextKeys } from 'vs/workbench/contrib/testing/common/testingContextKeys';
 import { ITestResult, LiveTestResult, TestResultItemChange, TestResultItemChangeReason } from 'vs/workbench/contrib/testing/common/testResult';
diff --git a/src/vs/workbench/contrib/testing/common/testStubs.ts b/src/vs/workbench/contrib/testing/common/testStubs.ts
index 8ef2b8768c8..efe93d92f67 100644
--- a/src/vs/workbench/contrib/testing/common/testStubs.ts
+++ b/src/vs/workbench/contrib/testing/common/testStubs.ts
@@ -28,14 +28,14 @@ export const testStubs = {
 		collection.root.label = 'root';
 		collection.resolveHandler = item => {
 			if (item === undefined) {
-				const a = new TestItemImpl(idPrefix + 'a', 'a', URI.file('/'));
+				const a = new TestItemImpl('ctrlId', idPrefix + 'a', 'a', URI.file('/'));
 				a.canResolveChildren = true;
-				const b = new TestItemImpl(idPrefix + 'b', 'b', URI.file('/'));
-				collection.root.children.set([a, b]);
+				const b = new TestItemImpl('ctrlId', idPrefix + 'b', 'b', URI.file('/'));
+				collection.root.children.replace([a, b]);
 			} else if (item.id === idPrefix + 'a') {
-				item.children.set([
-					new TestItemImpl(idPrefix + 'aa', 'aa', URI.file('/')),
-					new TestItemImpl(idPrefix + 'ab', 'ab', URI.file('/')),
+				item.children.replace([
+					new TestItemImpl('ctrlId', idPrefix + 'aa', 'aa', URI.file('/')),
+					new TestItemImpl('ctrlId', idPrefix + 'ab', 'ab', URI.file('/')),
 				]);
 			}
 		};
diff --git a/src/vs/workbench/contrib/testing/common/testingStates.ts b/src/vs/workbench/contrib/testing/common/testingStates.ts
index 84c9cf019fe..d0ebaed215c 100644
--- a/src/vs/workbench/contrib/testing/common/testingStates.ts
+++ b/src/vs/workbench/contrib/testing/common/testingStates.ts
@@ -3,9 +3,7 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import { TestResultState } from 'vs/workbench/api/common/extHostTypes';
-
-export { TestResultState } from 'vs/workbench/api/common/extHostTypes';
+import { TestResultState } from 'vs/workbench/contrib/testing/common/testCollection';
 
 export type TreeStateNode = { statusNode: true; state: TestResultState; priority: number };
 
diff --git a/src/vs/workbench/contrib/testing/test/browser/explorerProjections/hierarchalByLocation.test.ts b/src/vs/workbench/contrib/testing/test/browser/explorerProjections/hierarchalByLocation.test.ts
index 0816fe168ba..b6158e5ee62 100644
--- a/src/vs/workbench/contrib/testing/test/browser/explorerProjections/hierarchalByLocation.test.ts
+++ b/src/vs/workbench/contrib/testing/test/browser/explorerProjections/hierarchalByLocation.test.ts
@@ -6,9 +6,8 @@
 import * as assert from 'assert';
 import { Emitter } from 'vs/base/common/event';
 import { HierarchicalByLocationProjection } from 'vs/workbench/contrib/testing/browser/explorerProjections/hierarchalByLocation';
-import { TestDiffOpType, TestItemExpandState, TestResultItem } from 'vs/workbench/contrib/testing/common/testCollection';
+import { TestDiffOpType, TestItemExpandState, TestResultItem, TestResultState } from 'vs/workbench/contrib/testing/common/testCollection';
 import { TestId } from 'vs/workbench/contrib/testing/common/testId';
-import { TestResultState } from 'vs/workbench/contrib/testing/common/testingStates';
 import { TestResultItemChange, TestResultItemChangeReason } from 'vs/workbench/contrib/testing/common/testResult';
 import { Convert, TestItemImpl } from 'vs/workbench/contrib/testing/common/testStubs';
 import { TestTreeTestHarness } from 'vs/workbench/contrib/testing/test/browser/testObjectTree';
@@ -55,10 +54,10 @@ suite('Workbench - Testing Explorer Hierarchal by Location Projection', () => {
 		harness.flush();
 		harness.pushDiff([
 			TestDiffOpType.Add,
-			{ controllerId: 'ctrl2', parent: null, expand: TestItemExpandState.Expanded, item: Convert.TestItem.from(new TestItemImpl('c', 'c', undefined), 'ctrl2') },
+			{ controllerId: 'ctrl2', parent: null, expand: TestItemExpandState.Expanded, item: Convert.TestItem.from(new TestItemImpl('ctrl2', 'c', 'c', undefined)) },
 		], [
 			TestDiffOpType.Add,
-			{ controllerId: 'ctrl2', parent: new TestId(['ctrl2', 'c']).toString(), expand: TestItemExpandState.NotExpandable, item: Convert.TestItem.from(new TestItemImpl('c-a', 'ca', undefined), 'ctrl2') },
+			{ controllerId: 'ctrl2', parent: new TestId(['ctrl2', 'c']).toString(), expand: TestItemExpandState.NotExpandable, item: Convert.TestItem.from(new TestItemImpl('ctrl2', 'c-a', 'ca', undefined)) },
 		]);
 
 		assert.deepStrictEqual(harness.flush(), [
@@ -76,7 +75,7 @@ suite('Workbench - Testing Explorer Hierarchal by Location Projection', () => {
 			{ e: 'b' }
 		]);
 
-		harness.c.root.children.get('id-a')!.children.add(new TestItemImpl('ac', 'ac', undefined));
+		harness.c.root.children.get('id-a')!.children.add(new TestItemImpl('ctrlId', 'ac', 'ac', undefined));
 
 		assert.deepStrictEqual(harness.flush(), [
 			{ e: 'a', children: [{ e: 'aa' }, { e: 'ab' }, { e: 'ac' }] },
@@ -106,7 +105,7 @@ suite('Workbench - Testing Explorer Hierarchal by Location Projection', () => {
 		resultsService.getStateById = () => [undefined, resultInState(TestResultState.Failed)];
 
 		const resultInState = (state: TestResultState): TestResultItem => ({
-			item: Convert.TestItem.from(harness.c.tree.get(new TestId(['ctrlId', 'id-a']).toString())!.actual, 'ctrlId'),
+			item: Convert.TestItem.from(harness.c.tree.get(new TestId(['ctrlId', 'id-a']).toString())!.actual),
 			parent: 'id-root',
 			tasks: [],
 			retired: false,
diff --git a/src/vs/workbench/contrib/testing/test/browser/explorerProjections/hierarchalByName.test.ts b/src/vs/workbench/contrib/testing/test/browser/explorerProjections/hierarchalByName.test.ts
index 91578aeddc2..da9b5619182 100644
--- a/src/vs/workbench/contrib/testing/test/browser/explorerProjections/hierarchalByName.test.ts
+++ b/src/vs/workbench/contrib/testing/test/browser/explorerProjections/hierarchalByName.test.ts
@@ -43,10 +43,10 @@ suite('Workbench - Testing Explorer Hierarchal by Name Projection', () => {
 		harness.flush();
 		harness.pushDiff([
 			TestDiffOpType.Add,
-			{ controllerId: 'ctrl2', parent: null, expand: TestItemExpandState.Expanded, item: Convert.TestItem.from(new TestItemImpl('c', 'root2', undefined), 'ctrl2') },
+			{ controllerId: 'ctrl2', parent: null, expand: TestItemExpandState.Expanded, item: Convert.TestItem.from(new TestItemImpl('ctrl2', 'c', 'root2', undefined)) },
 		], [
 			TestDiffOpType.Add,
-			{ controllerId: 'ctrl2', parent: new TestId(['ctrl2', 'c']).toString(), expand: TestItemExpandState.NotExpandable, item: Convert.TestItem.from(new TestItemImpl('c-a', 'c', undefined), 'ctrl2') },
+			{ controllerId: 'ctrl2', parent: new TestId(['ctrl2', 'c']).toString(), expand: TestItemExpandState.NotExpandable, item: Convert.TestItem.from(new TestItemImpl('ctrl2', 'c-a', 'c', undefined)) },
 		]);
 
 		assert.deepStrictEqual(harness.flush(), [
@@ -58,7 +58,7 @@ suite('Workbench - Testing Explorer Hierarchal by Name Projection', () => {
 	test('updates nodes if they add children', async () => {
 		harness.flush();
 
-		harness.c.root.children.get('id-a')!.children.add(new TestItemImpl('ac', 'ac', undefined));
+		harness.c.root.children.get('id-a')!.children.add(new TestItemImpl('ctrl2', 'ac', 'ac', undefined));
 
 		assert.deepStrictEqual(harness.flush(), [
 			{ e: 'aa' },
@@ -80,7 +80,7 @@ suite('Workbench - Testing Explorer Hierarchal by Name Projection', () => {
 
 	test('swaps when node is no longer leaf', async () => {
 		harness.flush();
-		harness.c.root.children.get('id-b')!.children.add(new TestItemImpl('ba', 'ba', undefined));
+		harness.c.root.children.get('id-b')!.children.add(new TestItemImpl('ctrl2', 'ba', 'ba', undefined));
 
 		assert.deepStrictEqual(harness.flush(), [
 			{ e: 'aa' },
diff --git a/src/vs/workbench/contrib/testing/test/common/testResultService.test.ts b/src/vs/workbench/contrib/testing/test/common/testResultService.test.ts
index 209ea14cbd3..a0f0d507c1c 100644
--- a/src/vs/workbench/contrib/testing/test/common/testResultService.test.ts
+++ b/src/vs/workbench/contrib/testing/test/common/testResultService.test.ts
@@ -10,14 +10,13 @@ import { Lazy } from 'vs/base/common/lazy';
 import { MockContextKeyService } from 'vs/platform/keybinding/test/common/mockKeybindingService';
 import { NullLogService } from 'vs/platform/log/common/log';
 import { SingleUseTestCollection } from 'vs/workbench/contrib/testing/common/ownedTestCollection';
-import { ITestTaskState, ResolvedTestRunRequest, TestResultItem, TestRunProfileBitset } from 'vs/workbench/contrib/testing/common/testCollection';
+import { ITestTaskState, ResolvedTestRunRequest, TestResultItem, TestResultState, TestRunProfileBitset } from 'vs/workbench/contrib/testing/common/testCollection';
 import { TestProfileService } from 'vs/workbench/contrib/testing/common/testConfigurationService';
 import { TestId } from 'vs/workbench/contrib/testing/common/testId';
-import { TestResultState } from 'vs/workbench/contrib/testing/common/testingStates';
 import { HydratedTestResult, LiveOutputController, LiveTestResult, makeEmptyCounts, resultItemParents, TestResultItemChange, TestResultItemChangeReason } from 'vs/workbench/contrib/testing/common/testResult';
 import { TestResultService } from 'vs/workbench/contrib/testing/common/testResultService';
 import { InMemoryResultStorage, ITestResultStorage } from 'vs/workbench/contrib/testing/common/testResultStorage';
-import { Convert, getInitializedMainTestCollection, testStubs } from 'vs/workbench/contrib/testing/common/testStubs';
+import { Convert, getInitializedMainTestCollection, TestItemImpl, testStubs } from 'vs/workbench/contrib/testing/common/testStubs';
 import { TestStorageService } from 'vs/workbench/test/common/workbenchTestServices';
 
 export const emptyOutputController = () => new LiveOutputController(
@@ -65,14 +64,14 @@ suite('Workbench - Test Results Service', () => {
 		tests = testStubs.nested();
 		await tests.expand(tests.root.id, Infinity);
 		r.addTestChainToRun('ctrlId', [
-			Convert.TestItem.from(tests.root, 'ctrlId'),
-			Convert.TestItem.from(tests.root.children.get('id-a')!, 'ctrlId'),
-			Convert.TestItem.from(tests.root.children.get('id-a')!.children.get('id-aa')!, 'ctrlId'),
+			Convert.TestItem.from(tests.root),
+			Convert.TestItem.from(tests.root.children.get('id-a') as TestItemImpl),
+			Convert.TestItem.from(tests.root.children.get('id-a')!.children.get('id-aa') as TestItemImpl),
 		]);
 
 		r.addTestChainToRun('ctrlId', [
-			Convert.TestItem.from(tests.root.children.get('id-a')!, 'ctrlId'),
-			Convert.TestItem.from(tests.root.children.get('id-a')!.children.get('id-ab')!, 'ctrlId'),
+			Convert.TestItem.from(tests.root.children.get('id-a') as TestItemImpl),
+			Convert.TestItem.from(tests.root.children.get('id-a')!.children.get('id-ab') as TestItemImpl),
 		]);
 	});
 
diff --git a/src/vs/workbench/contrib/testing/test/common/testResultStorage.test.ts b/src/vs/workbench/contrib/testing/test/common/testResultStorage.test.ts
index 67d41de0bb6..218952e51ba 100644
--- a/src/vs/workbench/contrib/testing/test/common/testResultStorage.test.ts
+++ b/src/vs/workbench/contrib/testing/test/common/testResultStorage.test.ts
@@ -9,7 +9,7 @@ import { NullLogService } from 'vs/platform/log/common/log';
 import { TestId } from 'vs/workbench/contrib/testing/common/testId';
 import { ITestResult, LiveTestResult } from 'vs/workbench/contrib/testing/common/testResult';
 import { InMemoryResultStorage, RETAIN_MAX_RESULTS } from 'vs/workbench/contrib/testing/common/testResultStorage';
-import { Convert, testStubs } from 'vs/workbench/contrib/testing/common/testStubs';
+import { Convert, TestItemImpl, testStubs } from 'vs/workbench/contrib/testing/common/testStubs';
 import { emptyOutputController } from 'vs/workbench/contrib/testing/test/common/testResultService.test';
 import { TestStorageService } from 'vs/workbench/test/common/workbenchTestServices';
 
@@ -28,9 +28,9 @@ suite('Workbench - Test Result Storage', () => {
 		const tests = testStubs.nested();
 		tests.expand(tests.root.id, Infinity);
 		t.addTestChainToRun('ctrlId', [
-			Convert.TestItem.from(tests.root, 'ctrlId'),
-			Convert.TestItem.from(tests.root.children.get('id-a')!, 'ctrlId'),
-			Convert.TestItem.from(tests.root.children.get('id-a')!.children.get('id-aa')!, 'ctrlId'),
+			Convert.TestItem.from(tests.root),
+			Convert.TestItem.from(tests.root.children.get('id-a') as TestItemImpl),
+			Convert.TestItem.from(tests.root.children.get('id-a')!.children.get('id-aa') as TestItemImpl),
 		]);
 
 		if (addMessage) {
diff --git a/src/vs/workbench/test/browser/api/extHostTesting.test.ts b/src/vs/workbench/test/browser/api/extHostTesting.test.ts
index 3aa083acd84..222e5b31bc0 100644
--- a/src/vs/workbench/test/browser/api/extHostTesting.test.ts
+++ b/src/vs/workbench/test/browser/api/extHostTesting.test.ts
@@ -11,7 +11,7 @@ import { mockObject, MockObject } from 'vs/base/test/common/mock';
 import { MainThreadTestingShape } from 'vs/workbench/api/common/extHost.protocol';
 import { TestRunProfileImpl, TestRunCoordinator, TestRunDto } from 'vs/workbench/api/common/extHostTesting';
 import * as convert from 'vs/workbench/api/common/extHostTypeConverters';
-import { TestMessage, TestResultState, TestRunProfileGroup } from 'vs/workbench/api/common/extHostTypes';
+import { TestMessage, TestResultState, TestRunProfileKind } from 'vs/workbench/api/common/extHostTypes';
 import { TestDiffOpType, TestItemExpandState } from 'vs/workbench/contrib/testing/common/testCollection';
 import { TestId } from 'vs/workbench/contrib/testing/common/testId';
 import { TestItemImpl, testStubs } from 'vs/workbench/contrib/testing/common/testStubs';
@@ -74,24 +74,24 @@ suite('ExtHost Testing', () => {
 	suite('OwnedTestCollection', () => {
 		test('adds a root recursively', async () => {
 			await single.expand(single.root.id, Infinity);
-			const a = single.root.children.get('id-a')!;
-			const b = single.root.children.get('id-b')!;
+			const a = single.root.children.get('id-a') as TestItemImpl;
+			const b = single.root.children.get('id-b') as TestItemImpl;
 			assert.deepStrictEqual(single.collectDiff(), [
 				[
 					TestDiffOpType.Add,
-					{ controllerId: 'ctrlId', parent: null, expand: TestItemExpandState.BusyExpanding, item: { ...convert.TestItem.from(single.root, 'ctrlId') } }
+					{ controllerId: 'ctrlId', parent: null, expand: TestItemExpandState.BusyExpanding, item: { ...convert.TestItem.from(single.root) } }
 				],
 				[
 					TestDiffOpType.Add,
-					{ controllerId: 'ctrlId', parent: single.root.id, expand: TestItemExpandState.BusyExpanding, item: { ...convert.TestItem.from(a, 'ctrlId') } }
+					{ controllerId: 'ctrlId', parent: single.root.id, expand: TestItemExpandState.BusyExpanding, item: { ...convert.TestItem.from(a) } }
 				],
 				[
 					TestDiffOpType.Add,
-					{ controllerId: 'ctrlId', parent: new TestId(['ctrlId', 'id-a']).toString(), expand: TestItemExpandState.NotExpandable, item: convert.TestItem.from(a.children.get('id-aa')!, 'ctrlId') }
+					{ controllerId: 'ctrlId', parent: new TestId(['ctrlId', 'id-a']).toString(), expand: TestItemExpandState.NotExpandable, item: convert.TestItem.from(a.children.get('id-aa') as TestItemImpl) }
 				],
 				[
 					TestDiffOpType.Add,
-					{ controllerId: 'ctrlId', parent: new TestId(['ctrlId', 'id-a']).toString(), expand: TestItemExpandState.NotExpandable, item: convert.TestItem.from(a.children.get('id-ab')!, 'ctrlId') }
+					{ controllerId: 'ctrlId', parent: new TestId(['ctrlId', 'id-a']).toString(), expand: TestItemExpandState.NotExpandable, item: convert.TestItem.from(a.children.get('id-ab') as TestItemImpl) }
 				],
 				[
 					TestDiffOpType.Update,
@@ -99,7 +99,7 @@ suite('ExtHost Testing', () => {
 				],
 				[
 					TestDiffOpType.Add,
-					{ controllerId: 'ctrlId', parent: single.root.id, expand: TestItemExpandState.NotExpandable, item: convert.TestItem.from(b, 'ctrlId') }
+					{ controllerId: 'ctrlId', parent: single.root.id, expand: TestItemExpandState.NotExpandable, item: convert.TestItem.from(b) }
 				],
 				[
 					TestDiffOpType.Update,
@@ -153,7 +153,7 @@ suite('ExtHost Testing', () => {
 		test('adds new children', () => {
 			single.expand(single.root.id, Infinity);
 			single.collectDiff();
-			const child = new TestItemImpl('id-ac', 'c', undefined);
+			const child = new TestItemImpl('ctrlId', 'id-ac', 'c', undefined);
 			single.root.children.get('id-a')!.children.add(child);
 
 			assert.deepStrictEqual(single.collectDiff(), [
@@ -161,7 +161,7 @@ suite('ExtHost Testing', () => {
 					controllerId: 'ctrlId',
 					parent: new TestId(['ctrlId', 'id-a']).toString(),
 					expand: TestItemExpandState.NotExpandable,
-					item: convert.TestItem.from(child, 'ctrlId'),
+					item: convert.TestItem.from(child),
 				}],
 			]);
 			assert.deepStrictEqual(
@@ -176,11 +176,11 @@ suite('ExtHost Testing', () => {
 			single.collectDiff();
 
 			const oldA = single.root.children.get('id-a') as TestItemImpl;
-			const newA = new TestItemImpl('id-a', 'Hello world', undefined);
-			newA.children.set(oldA.children);
-			single.root.children.set([
+			const newA = new TestItemImpl('ctrlId', 'id-a', 'Hello world', undefined);
+			newA.children.replace([...oldA.children]);
+			single.root.children.replace([
 				newA,
-				new TestItemImpl('id-b', single.root.children.get('id-b')!.label, undefined),
+				new TestItemImpl('ctrlId', 'id-b', single.root.children.get('id-b')!.label, undefined),
 			]);
 
 			assert.deepStrictEqual(single.collectDiff(), [
@@ -207,12 +207,12 @@ suite('ExtHost Testing', () => {
 			single.collectDiff();
 
 			const oldA = single.root.children.get('id-a')!;
-			const newA = new TestItemImpl('id-a', single.root.children.get('id-a')!.label, undefined);
+			const newA = new TestItemImpl('ctrlId', 'id-a', single.root.children.get('id-a')!.label, undefined);
 			const oldAA = oldA.children.get('id-aa')!;
 			const oldAB = oldA.children.get('id-ab')!;
-			const newAB = new TestItemImpl('id-ab', 'Hello world', undefined);
-			newA.children.set([oldAA, newAB]);
-			single.root.children.set([newA, single.root.children.get('id-b')!]);
+			const newAB = new TestItemImpl('ctrlId', 'id-ab', 'Hello world', undefined);
+			newA.children.replace([oldAA, newAB]);
+			single.root.children.replace([newA, single.root.children.get('id-b')!]);
 
 			assert.deepStrictEqual(single.collectDiff(), [
 				[
@@ -247,8 +247,8 @@ suite('ExtHost Testing', () => {
 		test('moves an item to be a new child', async () => {
 			await single.expand(single.root.id, 0);
 			single.collectDiff();
-			const b = single.root.children.get('id-b')!;
-			const a = single.root.children.get('id-a')!;
+			const b = single.root.children.get('id-b') as TestItemImpl;
+			const a = single.root.children.get('id-a') as TestItemImpl;
 			a.children.add(b);
 			assert.deepStrictEqual(single.collectDiff(), [
 				[
@@ -257,7 +257,7 @@ suite('ExtHost Testing', () => {
 				],
 				[
 					TestDiffOpType.Add,
-					{ controllerId: 'ctrlId', parent: new TestId(['ctrlId', 'id-a']).toString(), expand: TestItemExpandState.NotExpandable, item: convert.TestItem.from(b, 'ctrlId') }
+					{ controllerId: 'ctrlId', parent: new TestId(['ctrlId', 'id-a']).toString(), expand: TestItemExpandState.NotExpandable, item: convert.TestItem.from(b) }
 				],
 			]);
 
@@ -426,7 +426,7 @@ suite('ExtHost Testing', () => {
 			cts = new CancellationTokenSource();
 			c = new TestRunCoordinator(proxy);
 
-			configuration = new TestRunProfileImpl(mockObject<MainThreadTestingShape, {}>(), 'ctrlId', 42, 'Do Run', TestRunProfileGroup.Run, () => { }, false);
+			configuration = new TestRunProfileImpl(mockObject<MainThreadTestingShape, {}>(), 'ctrlId', 42, 'Do Run', TestRunProfileKind.Run, () => { }, false);
 
 			await single.expand(single.root.id, Infinity);
 			single.collectDiff();
@@ -509,9 +509,9 @@ suite('ExtHost Testing', () => {
 				'ctrl',
 				tracker.id,
 				[
-					convert.TestItem.from(single.root, 'ctrlId'),
-					convert.TestItem.from(single.root.children.get('id-a')!, 'ctrlId'),
-					convert.TestItem.from(single.root.children.get('id-a')!.children.get('id-aa')!, 'ctrlId'),
+					convert.TestItem.from(single.root),
+					convert.TestItem.from(single.root.children.get('id-a') as TestItemImpl),
+					convert.TestItem.from(single.root.children.get('id-a')!.children.get('id-aa') as TestItemImpl),
 				]
 			]);
 			assert.deepStrictEqual(proxy.$addTestsToRun.args, expectedArgs);
@@ -522,8 +522,8 @@ suite('ExtHost Testing', () => {
 				'ctrl',
 				tracker.id,
 				[
-					convert.TestItem.from(single.root.children.get('id-a')!, 'ctrlId'),
-					convert.TestItem.from(single.root.children.get('id-a')!.children.get('id-ab')!, 'ctrlId'),
+					convert.TestItem.from(single.root.children.get('id-a') as TestItemImpl),
+					convert.TestItem.from(single.root.children.get('id-a')!.children.get('id-ab') as TestItemImpl),
 				],
 			]);
 			assert.deepStrictEqual(proxy.$addTestsToRun.args, expectedArgs);