test(daemon): Add mutex unit tests (merge #2122)

Adds tests for `daemon/src/mutex.js`.

packages/daemon/test/test-mutex.js

@@ -0,0 +1,93 @@
+/* global setTimeout */
+import '@endo/init/debug.js';
+
+import rawTest from 'ava';
+import { wrapTest } from '@endo/ses-ava';
+
+import { makeMutex } from '../src/mutex.js';
+
+const test = wrapTest(rawTest);
+
+const delay = () => new Promise(resolve => setTimeout(resolve, 1));
+
+test('releases lock in expected order (sync functions)', async t => {
+  const mutex = makeMutex();
+  const results = [];
+
+  await Promise.all([
+    mutex.enqueue(() => {
+      results.push(1);
+    }),
+    mutex.enqueue(() => {
+      results.push(2);
+    }),
+    mutex.enqueue(() => {
+      results.push(3);
+    }),
+  ]);
+
+  t.deepEqual(results, [1, 2, 3]);
+});
+
+test('releases lock in expected order (async functions)', async t => {
+  const mutex = makeMutex();
+  const results = [];
+
+  await Promise.all([
+    mutex.enqueue(async () => {
+      results.push(1);
+    }),
+    mutex.enqueue(async () => {
+      results.push(2);
+    }),
+    mutex.enqueue(async () => {
+      results.push(3);
+    }),
+  ]);
+
+  t.deepEqual(results, [1, 2, 3]);
+});
+
+test('releases lock in expected order (async functions with await)', async t => {
+  const mutex = makeMutex();
+  const results = [];
+
+  await Promise.all([
+    mutex.enqueue(async () => {
+      await delay();
+      results.push(1);
+    }),
+    mutex.enqueue(async () => {
+      await delay();
+      results.push(2);
+    }),
+    mutex.enqueue(async () => {
+      await delay();
+      results.push(3);
+    }),
+  ]);
+
+  t.deepEqual(results, [1, 2, 3]);
+});
+
+test('immediately releases the lock to the awaiter', async t => {
+  const mutex = makeMutex();
+  const results = [];
+
+  await Promise.all([
+    mutex.enqueue(async () => {
+      await delay();
+      results.push(2);
+    }),
+    (async () => {
+      results.push(1);
+      await mutex.enqueue(() => delay());
+      results.push(3);
+    })(),
+    mutex.enqueue(async () => {
+      results.push(4);
+    }),
+  ]);
+
+  t.deepEqual(results, [1, 2, 3, 4]);
+});