Stabilise Vitest MatrixChat test (#34555)

* Stabilise Vitest MatrixChat test

* Ignore post-teardown exceptions in vitest

* Iterate

apps/web/src/components/views/elements/LanguageDropdown.tsx

@@ -39,6 +39,8 @@ interface IState {
 }
 
 export default class LanguageDropdown extends React.Component<IProps, IState> {
+    private unmounted = false;
+
     public constructor(props: IProps) {
         super(props);
 
@@ -49,8 +51,11 @@ export default class LanguageDropdown extends React.Component<IProps, IState> {
     }
 
     public componentDidMount(): void {
+        this.unmounted = false;
+
         getAllLanguagesWithLabels()
             .then((langs) => {
+                if (this.unmounted) return;
                 langs.sort(function (a, b) {
                     if (a.labelInTargetLanguage < b.labelInTargetLanguage) return -1;
                     if (a.labelInTargetLanguage > b.labelInTargetLanguage) return 1;
@@ -59,6 +64,7 @@ export default class LanguageDropdown extends React.Component<IProps, IState> {
                 this.setState({ langs });
             })
             .catch(() => {
+                if (this.unmounted) return;
                 this.setState({
                     langs: [
                         {
@@ -78,6 +84,10 @@ export default class LanguageDropdown extends React.Component<IProps, IState> {
         }
     }
 
+    public componentWillUnmount(): void {
+        this.unmounted = true;
+    }
+
     private onSearchChange = (search: string): void => {
         this.setState({
             searchQuery: search,

apps/web/src/test/setupTests.ts

@@ -18,9 +18,26 @@ declare global {
 
 globalThis.IS_REACT_ACT_ENVIRONMENT = true;
 
+// Ignore benign post-teardown exceptions as they cause flakes
+const guardState = globalThis as unknown as { __vitestTestRunning?: boolean; __teardownGuardInstalled?: boolean };
+if (!guardState.__teardownGuardInstalled) {
+    guardState.__teardownGuardInstalled = true;
+    const isPostTeardownStraggler = (): boolean => !guardState.__vitestTestRunning || typeof window === "undefined";
+    process.on("uncaughtException", (err) => {
+        if (isPostTeardownStraggler()) return;
+        throw err;
+    });
+    process.on("unhandledRejection", (reason) => {
+        if (isPostTeardownStraggler()) return;
+        throw reason;
+    });
+}
+
 manageFetchMockGlobally();
 
 beforeEach(() => {
+    guardState.__vitestTestRunning = true;
+
     vi.stubEnv("TZ", "UTC");
 
     // set up fetch API mock
@@ -31,7 +48,10 @@ beforeEach(() => {
     setupLanguageMock();
 });
 
-afterEach(() => fetchMock.callHistory.flush());
+afterEach(() => {
+    guardState.__vitestTestRunning = false;
+    return fetchMock.callHistory.flush();
+});
 
 // uninitialised SdkConfig causes lots of warnings in console, init with defaults
 SdkConfig.put(DEFAULTS);