Use async/await in env var tests and improve polling

Fixes #120077

extensions/vscode-api-tests/src/utils.ts

@@ -4,6 +4,7 @@
  *--------------------------------------------------------------------------------------------*/
 
 import * as assert from 'assert';
+import { EOL } from 'os';
 import * as vscode from 'vscode';
 import { TestFS } from './memfs';
 
@@ -149,3 +150,35 @@ export function suiteRepeat(n: number, description: string, callback: (this: any
 		suite(`${description} (iteration ${i})`, callback);
 	}
 }
+
+export async function poll<T>(
+	fn: () => Thenable<T>,
+	acceptFn: (result: T) => boolean,
+	timeoutMessage: string,
+	retryCount: number = 200,
+	retryInterval: number = 100 // millis
+): Promise<T> {
+	let trial = 1;
+	let lastError: string = '';
+
+	while (true) {
+		if (trial > retryCount) {
+			throw new Error(`Timeout: ${timeoutMessage} after ${(retryCount * retryInterval) / 1000} seconds.\r${lastError}`);
+		}
+
+		let result;
+		try {
+			result = await fn();
+			if (acceptFn(result)) {
+				return result;
+			} else {
+				lastError = 'Did not pass accept function';
+			}
+		} catch (e: any) {
+			lastError = Array.isArray(e.stack) ? e.stack.join(EOL) : e.stack;
+		}
+
+		await new Promise(resolve => setTimeout(resolve, retryInterval));
+		trial++;
+	}
+}