add back tests for flattenAsyncIterable

this was not restored when we restored subscription support (conditioned on an argument)

packages/executor/src/execution/__tests__/flattenAsyncIterable-test.ts

@@ -0,0 +1,146 @@
+import { flattenAsyncIterable } from '../flattenAsyncIterable.js';
+
+describe('flattenAsyncIterable', () => {
+  it('flatten nested async generators', async () => {
+    async function* source() {
+      yield await Promise.resolve(
+        (async function* nested(): AsyncGenerator<number, void, void> {
+          yield await Promise.resolve(1.1);
+          yield await Promise.resolve(1.2);
+        })(),
+      );
+      yield await Promise.resolve(
+        (async function* nested(): AsyncGenerator<number, void, void> {
+          yield await Promise.resolve(2.1);
+          yield await Promise.resolve(2.2);
+        })(),
+      );
+    }
+
+    const doubles = flattenAsyncIterable(source());
+
+    const result = [];
+    for await (const x of doubles) {
+      result.push(x);
+    }
+    expect(result).toEqual([1.1, 1.2, 2.1, 2.2]);
+  });
+
+  it('allows returning early from a nested async generator', async () => {
+    async function* source() {
+      yield await Promise.resolve(
+        (async function* nested(): AsyncGenerator<number, void, void> {
+          yield await Promise.resolve(1.1);
+          yield await Promise.resolve(1.2);
+        })(),
+      );
+      yield await Promise.resolve(
+        (async function* nested(): AsyncGenerator<number, void, void> {
+          yield await Promise.resolve(2.1); /* c8 ignore start */
+          // Not reachable, early return
+          yield await Promise.resolve(2.2);
+        })(),
+      );
+      // Not reachable, early return
+      yield await Promise.resolve(
+        (async function* nested(): AsyncGenerator<number, void, void> {
+          yield await Promise.resolve(3.1);
+          yield await Promise.resolve(3.2);
+        })(),
+      );
+    }
+    /* c8 ignore stop */
+
+    const doubles = flattenAsyncIterable(source());
+
+    expect(await doubles.next()).toEqual({ value: 1.1, done: false });
+    expect(await doubles.next()).toEqual({ value: 1.2, done: false });
+    expect(await doubles.next()).toEqual({ value: 2.1, done: false });
+
+    // Early return
+    expect(await doubles.return()).toEqual({
+      value: undefined,
+      done: true,
+    });
+
+    // Subsequent next calls
+    expect(await doubles.next()).toEqual({
+      value: undefined,
+      done: true,
+    });
+    expect(await doubles.next()).toEqual({
+      value: undefined,
+      done: true,
+    });
+  });
+
+  it('allows throwing errors from a nested async generator', async () => {
+    async function* source() {
+      yield await Promise.resolve(
+        (async function* nested(): AsyncGenerator<number, void, void> {
+          yield await Promise.resolve(1.1);
+          yield await Promise.resolve(1.2);
+        })(),
+      );
+      yield await Promise.resolve(
+        (async function* nested(): AsyncGenerator<number, void, void> {
+          yield await Promise.resolve(2.1); /* c8 ignore start */
+          // Not reachable, early return
+          yield await Promise.resolve(2.2);
+        })(),
+      );
+      // Not reachable, early return
+      yield await Promise.resolve(
+        (async function* nested(): AsyncGenerator<number, void, void> {
+          yield await Promise.resolve(3.1);
+          yield await Promise.resolve(3.2);
+        })(),
+      );
+    }
+    /* c8 ignore stop */
+
+    const doubles = flattenAsyncIterable(source());
+
+    expect(await doubles.next()).toEqual({ value: 1.1, done: false });
+    expect(await doubles.next()).toEqual({ value: 1.2, done: false });
+    expect(await doubles.next()).toEqual({ value: 2.1, done: false });
+
+    // Throw error
+    let caughtError;
+    try {
+      await doubles.throw('ouch'); /* c8 ignore start */
+    } catch (e) {
+      caughtError = e;
+    }
+    expect(caughtError).toEqual('ouch');
+  });
+  it('completely yields sub-iterables even when next() called in parallel', async () => {
+    async function* source() {
+      yield await Promise.resolve(
+        (async function* nested(): AsyncGenerator<number, void, void> {
+          yield await Promise.resolve(1.1);
+          yield await Promise.resolve(1.2);
+        })(),
+      );
+      yield await Promise.resolve(
+        (async function* nested(): AsyncGenerator<number, void, void> {
+          yield await Promise.resolve(2.1);
+          yield await Promise.resolve(2.2);
+        })(),
+      );
+    }
+
+    const result = flattenAsyncIterable(source());
+
+    const promise1 = result.next();
+    const promise2 = result.next();
+    expect(await promise1).toEqual({ value: 1.1, done: false });
+    expect(await promise2).toEqual({ value: 1.2, done: false });
+    expect(await result.next()).toEqual({ value: 2.1, done: false });
+    expect(await result.next()).toEqual({ value: 2.2, done: false });
+    expect(await result.next()).toEqual({
+      value: undefined,
+      done: true,
+    });
+  });
+});