platform/sandbox/reactivex/test/transformers/backpressure/buffer_test.dart

import 'dart:async';

import 'package:angel3_reactivex/angel3_reactivex.dart';
import 'package:test/test.dart';

import '../../utils.dart';

Stream<int> getStream(int n) async* {
  var k = 0;

  while (k < n) {
    await Future<void>.delayed(const Duration(milliseconds: 100));

    yield k++;
  }
}

void main() {
  test('Rx.buffer', () async {
    await expectLater(
        getStream(4).buffer(
            Stream<void>.periodic(const Duration(milliseconds: 160)).take(3)),
        emitsInOrder(<dynamic>[
          const [0, 1],
          const [2, 3],
          emitsDone
        ]));
  });

  test('Rx.buffer.sampleBeforeEvent.shouldEmit', () async {
    await expectLater(
        Stream.fromFuture(
            Future<void>.delayed(const Duration(milliseconds: 200))
                .then((_) => 'end')).startWith('start').buffer(
            Stream<void>.periodic(const Duration(milliseconds: 40)).take(10)),
        emitsInOrder(<dynamic>[
          const ['start'], // after 40ms
          const <String>[], // 80ms
          const <String>[], // 120ms
          const <String>[], // 160ms
          const ['end'], // done
          emitsDone
        ]));
  });

  test('Rx.buffer.shouldClose', () async {
    final controller = StreamController<int>()
      ..add(0)
      ..add(1)
      ..add(2)
      ..add(3);

    scheduleMicrotask(controller.close);

    await expectLater(
        controller.stream
            .buffer(Stream<void>.periodic(const Duration(seconds: 3)))
            .take(1),
        emitsInOrder(<dynamic>[
          const [0, 1, 2, 3], // done
          emitsDone
        ]));
  });

  test('Rx.buffer.reusable', () async {
    final transformer = BufferStreamTransformer<int>((_) =>
        Stream<void>.periodic(const Duration(milliseconds: 160))
            .take(3)
            .asBroadcastStream());

    await expectLater(
        getStream(4).transform(transformer),
        emitsInOrder(<dynamic>[
          const [0, 1],
          const [2, 3],
          emitsDone
        ]));

    await expectLater(
        getStream(4).transform(transformer),
        emitsInOrder(<dynamic>[
          const [0, 1],
          const [2, 3],
          emitsDone
        ]));
  });

  test('Rx.buffer.asBroadcastStream', () async {
    final stream = getStream(4).asBroadcastStream().buffer(
        Stream<void>.periodic(const Duration(milliseconds: 160))
            .take(10)
            .asBroadcastStream());

    // listen twice on same stream
    await expectLater(
        stream,
        emitsInOrder(<dynamic>[
          const [0, 1],
          const [2, 3],
          emitsDone
        ]));

    await expectLater(stream, emitsInOrder(<dynamic>[emitsDone]));
  });

  test('Rx.buffer.error.shouldThrowA', () async {
    await expectLater(
        Stream<void>.error(Exception())
            .buffer(Stream<void>.periodic(const Duration(milliseconds: 160))),
        emitsError(isException));
  });

  test('Rx.buffer.nullable', () {
    nullableTest<List<String?>>(
      (s) => s.buffer(Stream<void>.empty()),
    );
  });
}