main.dart

import 'dart:async';

import 'package:flutter_test/flutter_test.dart';

void main() {
  test('test case', () async {
    await expectLater(
      // create stream that emit Completer, and wait it
      ((() async* {
        try {
          final completer = Completer<void>();
          yield completer;
          await completer.future;
        } catch (_) {
          // handle error
        }
      })())
          .map((event) {
        // add error to completer
        event.completeError(Exception());

        return event;
      }),
      emitsThrough(anything),
    );
  });
}