diff --git a/Extension/test/scenarios/SingleRootProject/tests/buildAndDebug.test.ts b/Extension/test/scenarios/SingleRootProject/tests/buildAndDebug.test.ts
index 9f84df5e8..22182b48c 100644
--- a/Extension/test/scenarios/SingleRootProject/tests/buildAndDebug.test.ts
+++ b/Extension/test/scenarios/SingleRootProject/tests/buildAndDebug.test.ts
@@ -4,10 +4,25 @@
  * ------------------------------------------------------------------------------------------ */
 
 import * as assert from 'assert';
+import * as fs from 'fs';
 import { suite, test } from 'mocha';
+import * as os from 'os';
+import * as path from 'path';
 import * as vscode from 'vscode';
 import { updateBuildAndDebugSessionState } from '../../../../src/Debugger/extension';
 import { SessionState } from '../../../../src/sessionState';
+import * as testHelpers from '../../../common/testHelpers';
+
+async function assertSessionState(isSourceFile: boolean, isFolderOpen: boolean): Promise<void> {
+    const timeout: number = Date.now() + 1000;
+    while (Date.now() < timeout &&
+        (SessionState.buildAndDebugIsSourceFile.get() !== isSourceFile ||
+            SessionState.buildAndDebugIsFolderOpen.get() !== isFolderOpen)) {
+        await testHelpers.delay(10);
+    }
+    assert.strictEqual(SessionState.buildAndDebugIsSourceFile.get(), isSourceFile);
+    assert.strictEqual(SessionState.buildAndDebugIsFolderOpen.get(), isFolderOpen);
+}
 
 suite("BuildAndDebug SessionState Tests", () => {
     test("updateBuildAndDebugSessionState sets false when editor is undefined", () => {
@@ -41,6 +56,40 @@ suite("BuildAndDebug SessionState Tests", () => {
         assert.strictEqual(SessionState.buildAndDebugIsFolderOpen.get(), true);
     });
 
+    test("updateBuildAndDebugSessionState tracks an external C/C++ source file", () => {
+        const workspaceFolder = vscode.workspace.workspaceFolders?.[0] ?? assert.fail("No workspace folder available");
+        const mockEditor: any = {
+            document: {
+                uri: vscode.Uri.joinPath(workspaceFolder.uri, "..", "external.cpp"),
+                languageId: "cpp"
+            }
+        };
+        updateBuildAndDebugSessionState(mockEditor);
+        assert.strictEqual(SessionState.buildAndDebugIsSourceFile.get(), true);
+        assert.strictEqual(SessionState.buildAndDebugIsFolderOpen.get(), false);
+    });
+
+    test("active document language changes update session state", async () => {
+        const temporaryDirectory: string = await fs.promises.mkdtemp(path.join(os.tmpdir(), "cpptools-build-and-debug-"));
+        const sourceUri: vscode.Uri = vscode.Uri.file(path.join(temporaryDirectory, "external.cpp"));
+        await fs.promises.writeFile(sourceUri.fsPath, "int main() { return 0; }\n");
+
+        try {
+            let document: vscode.TextDocument = await vscode.workspace.openTextDocument(sourceUri);
+            await vscode.window.showTextDocument(document);
+            await assertSessionState(true, false);
+
+            document = await vscode.languages.setTextDocumentLanguage(document, "plaintext");
+            await assertSessionState(false, true);
+
+            await vscode.languages.setTextDocumentLanguage(document, "cpp");
+            await assertSessionState(true, false);
+        } finally {
+            await vscode.commands.executeCommand("workbench.action.closeActiveEditor");
+            await fs.promises.rm(temporaryDirectory, { recursive: true, force: true });
+        }
+    });
+
     test("updateBuildAndDebugSessionState sets false for C/C++ header file", () => {
         const workspaceFolder = vscode.workspace.workspaceFolders?.[0] ?? assert.fail("No workspace folder available");
         const mockEditor: any = {