📝 Commit Details:

backend/node_modules/preact/test-utils/src/index.d.ts

@@ -0,0 +1,3 @@
+export function setupRerender(): () => void;
+export function act(callback: () => void | Promise<void>): Promise<void>;
+export function teardown(): void;

backend/node_modules/preact/test-utils/src/index.js

@@ -0,0 +1,118 @@
+import { options } from 'preact';
+
+/**
+ * Setup a rerender function that will drain the queue of pending renders
+ * @returns {() => void}
+ */
+export function setupRerender() {
+	options.__test__previousDebounce = options.debounceRendering;
+	options.debounceRendering = cb => (options.__test__drainQueue = cb);
+	return () => options.__test__drainQueue && options.__test__drainQueue();
+}
+
+const isThenable = value => value != null && typeof value.then == 'function';
+
+/** Depth of nested calls to `act`. */
+let actDepth = 0;
+
+/**
+ * Run a test function, and flush all effects and rerenders after invoking it.
+ *
+ * Returns a Promise which resolves "immediately" if the callback is
+ * synchronous or when the callback's result resolves if it is asynchronous.
+ *
+ * @param {() => void|Promise<void>} cb The function under test. This may be sync or async.
+ * @return {Promise<void>}
+ */
+export function act(cb) {
+	if (++actDepth > 1) {
+		// If calls to `act` are nested, a flush happens only when the
+		// outermost call returns. In the inner call, we just execute the
+		// callback and return since the infrastructure for flushing has already
+		// been set up.
+		//
+		// If an exception occurs, the outermost `act` will handle cleanup.
+		const result = cb();
+		if (isThenable(result)) {
+			return result.then(() => {
+				--actDepth;
+			});
+		}
+		--actDepth;
+		return Promise.resolve();
+	}
+
+	const previousRequestAnimationFrame = options.requestAnimationFrame;
+	const rerender = setupRerender();
+
+	/** @type {() => void} */
+	let flush, toFlush;
+
+	// Override requestAnimationFrame so we can flush pending hooks.
+	options.requestAnimationFrame = fc => (flush = fc);
+
+	const finish = () => {
+		try {
+			rerender();
+			while (flush) {
+				toFlush = flush;
+				flush = null;
+
+				toFlush();
+				rerender();
+			}
+		} catch (e) {
+			if (!err) {
+				err = e;
+			}
+		} finally {
+			teardown();
+		}
+
+		options.requestAnimationFrame = previousRequestAnimationFrame;
+		--actDepth;
+	};
+
+	let err;
+	let result;
+
+	try {
+		result = cb();
+	} catch (e) {
+		err = e;
+	}
+
+	if (isThenable(result)) {
+		return result.then(finish, err => {
+			finish();
+			throw err;
+		});
+	}
+
+	// nb. If the callback is synchronous, effects must be flushed before
+	// `act` returns, so that the caller does not have to await the result,
+	// even though React recommends this.
+	finish();
+	if (err) {
+		throw err;
+	}
+	return Promise.resolve();
+}
+
+/**
+ * Teardown test environment and reset preact's internal state
+ */
+export function teardown() {
+	if (options.__test__drainQueue) {
+		// Flush any pending updates leftover by test
+		options.__test__drainQueue();
+		delete options.__test__drainQueue;
+	}
+
+	if (typeof options.__test__previousDebounce != 'undefined') {
+		options.debounceRendering = options.__test__previousDebounce;
+		delete options.__test__previousDebounce;
+	} else {
+		options.debounceRendering = undefined;
+	}
+}