Flush all watchers on empty queue

ts/test-both/util/batcher_test.ts

@@ -0,0 +1,91 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+import * as sinon from 'sinon';
+
+import { createBatcher } from '../../util/batcher';
+import { sleep } from '../../util/sleep';
+
+describe('batcher', () => {
+  it('should schedule a full batch', async () => {
+    const processBatch = sinon.fake.resolves(undefined);
+
+    const batcher = createBatcher<number>({
+      name: 'test',
+      wait: 10,
+      maxSize: 2,
+      processBatch,
+    });
+
+    batcher.add(1);
+    batcher.add(2);
+
+    assert.ok(processBatch.calledOnceWith([1, 2]), 'Full batch on first call');
+  });
+
+  it('should schedule a partial batch', async () => {
+    const processBatch = sinon.fake.resolves(undefined);
+
+    const batcher = createBatcher<number>({
+      name: 'test',
+      wait: 5,
+      maxSize: 2,
+      processBatch,
+    });
+
+    batcher.add(1);
+
+    await sleep(10);
+
+    assert.ok(processBatch.calledOnceWith([1]), 'Partial batch after timeout');
+  });
+
+  it('should flushAndWait a partial batch', async () => {
+    const processBatch = sinon.fake.resolves(undefined);
+
+    const batcher = createBatcher<number>({
+      name: 'test',
+      wait: 10000,
+      maxSize: 1000,
+      processBatch,
+    });
+
+    batcher.add(1);
+
+    await batcher.flushAndWait();
+
+    assert.ok(
+      processBatch.calledOnceWith([1]),
+      'Partial batch after flushAndWait'
+    );
+  });
+
+  it('should flushAndWait a partial batch with new items added', async () => {
+    let calledTimes = 0;
+    const processBatch = async (batch: Array<number>): Promise<void> => {
+      calledTimes += 1;
+      if (calledTimes === 1) {
+        assert.deepEqual(batch, [1], 'First partial batch');
+        batcher.add(2);
+      } else if (calledTimes === 2) {
+        assert.deepEqual(batch, [2], 'Second partial batch');
+      } else {
+        assert.strictEqual(calledTimes, 2);
+      }
+    };
+
+    const batcher = createBatcher<number>({
+      name: 'test',
+      wait: 10000,
+      maxSize: 1000,
+      processBatch,
+    });
+
+    batcher.add(1);
+
+    await batcher.flushAndWait();
+
+    assert.strictEqual(calledTimes, 2);
+  });
+});