diff --git a/src/vs/code/electron-main/window.ts b/src/vs/code/electron-main/window.ts
index a26de77fea4..56ac66e4c3c 100644
--- a/src/vs/code/electron-main/window.ts
+++ b/src/vs/code/electron-main/window.ts
@@ -30,6 +30,7 @@ export interface IWindowState {
 export interface IWindowCreationOptions {
 	state: IWindowState;
 	extensionDevelopmentPath?: string;
+	isExtensionTestHost?: boolean;
 	allowFullscreen?: boolean;
 	titleBarStyle?: 'native' | 'custom';
 }
@@ -139,6 +140,7 @@ export class VSCodeWindow implements IVSCodeWindow {
 	private _lastFocusTime: number;
 	private _readyState: ReadyState;
 	private _extensionDevelopmentPath: string;
+	private _isExtensionTestHost: boolean;
 	private windowState: IWindowState;
 	private currentWindowMode: WindowMode;
 
@@ -158,6 +160,7 @@ export class VSCodeWindow implements IVSCodeWindow {
 		this._lastFocusTime = -1;
 		this._readyState = ReadyState.NONE;
 		this._extensionDevelopmentPath = config.extensionDevelopmentPath;
+		this._isExtensionTestHost = config.isExtensionTestHost;
 		this.whenReadyCallbacks = [];
 
 		// Load window state
@@ -242,10 +245,14 @@ export class VSCodeWindow implements IVSCodeWindow {
 		return this.hiddenTitleBarStyle;
 	}
 
-	public get isPluginDevelopmentHost(): boolean {
+	public get isExtensionDevelopmentHost(): boolean {
 		return !!this._extensionDevelopmentPath;
 	}
 
+	public get isExtensionTestHost(): boolean {
+		return this._isExtensionTestHost;
+	}
+
 	public get extensionDevelopmentPath(): string {
 		return this._extensionDevelopmentPath;
 	}
@@ -444,7 +451,7 @@ export class VSCodeWindow implements IVSCodeWindow {
 
 		// Some configuration things get inherited if the window is being reloaded and we are
 		// in plugin development mode. These options are all development related.
-		if (this.isPluginDevelopmentHost && cli) {
+		if (this.isExtensionDevelopmentHost && cli) {
 			configuration.verbose = cli.verbose;
 			configuration.debugPluginHost = cli.debugPluginHost;
 			configuration.debugBrkPluginHost = cli.debugBrkPluginHost;
diff --git a/src/vs/code/electron-main/windows.ts b/src/vs/code/electron-main/windows.ts
index 7735e5d527f..464606f20a2 100644
--- a/src/vs/code/electron-main/windows.ts
+++ b/src/vs/code/electron-main/windows.ts
@@ -237,7 +237,7 @@ export class WindowsManager implements IWindowsMainService {
 			}
 
 			// 2-N windows open: Keep a list of windows that are opened on a specific folder to restore it in the next session as needed
-			this.windowsState.openedFolders = WindowsManager.WINDOWS.filter(w => w.readyState === ReadyState.READY && !!w.openedWorkspacePath && !w.isPluginDevelopmentHost).map(w => {
+			this.windowsState.openedFolders = WindowsManager.WINDOWS.filter(w => w.readyState === ReadyState.READY && !!w.openedWorkspacePath && !w.isExtensionDevelopmentHost).map(w => {
 				return <IWindowState>{
 					workspacePath: w.openedWorkspacePath,
 					uiState: w.serializeWindowState()
@@ -456,7 +456,7 @@ export class WindowsManager implements IWindowsMainService {
 
 		// Remember in recent document list (unless this opens for extension development)
 		// Also do not add paths when files are opened for diffing, only if opened individually
-		if (!usedWindows.some(w => w.isPluginDevelopmentHost) && !openConfig.cli.diff) {
+		if (!usedWindows.some(w => w.isExtensionDevelopmentHost) && !openConfig.cli.diff) {
 			const recentPaths: { path: string; isFile?: boolean; }[] = [];
 
 			iPathsToOpen.forEach(iPath => {
@@ -727,6 +727,7 @@ export class WindowsManager implements IWindowsMainService {
 			vscodeWindow = new VSCodeWindow({
 				state: this.getNewWindowState(configuration),
 				extensionDevelopmentPath: configuration.extensionDevelopmentPath,
+				isExtensionTestHost: !!configuration.extensionTestsPath,
 				allowFullscreen: this.lifecycleService.wasUpdated || (windowConfig && windowConfig.restoreFullscreen),
 				titleBarStyle: windowConfig ? windowConfig.titleBarStyle : void 0
 			},
@@ -1090,8 +1091,10 @@ export class WindowsManager implements IWindowsMainService {
 
 		// On Window close, update our stored state of this window
 		const state: IWindowState = { workspacePath: win.openedWorkspacePath, uiState: win.serializeWindowState() };
-		if (win.isPluginDevelopmentHost) {
-			this.windowsState.lastPluginDevelopmentHostWindow = state;
+		if (win.isExtensionDevelopmentHost) {
+			if (!win.isExtensionTestHost) {
+				this.windowsState.lastPluginDevelopmentHostWindow = state; // do not let test run window state overwrite our extension development state
+			}
 		} else {
 			this.windowsState.lastActiveWindow = state;
 
@@ -1225,7 +1228,7 @@ export class WindowsManager implements IWindowsMainService {
 		// If the user selected to exit from an extension development host window, do not quit, but just
 		// close the window unless this is the last window that is opened.
 		const vscodeWindow = this.getFocusedWindow();
-		if (vscodeWindow && vscodeWindow.isPluginDevelopmentHost && this.getWindowCount() > 1) {
+		if (vscodeWindow && vscodeWindow.isExtensionDevelopmentHost && this.getWindowCount() > 1) {
 			vscodeWindow.win.close();
 		}