RxJs Marble Test Fails When Using Observable.fromPromise - unit-testing

Question

I have been attempting to write an RxJS marble test for a simple redux-observable epic but cannot get it to pass. It appears that using fromPromise in the observable chain under test does not emit the items per the expected marble sequence when flush is called on the testScheduler.
Providing a sample of the test. If I replace Observable.fromPromise to Observable.of the test will pass.
Any insight is appreciated. RxJS 5 / redux-observable 0.18
...
const MY_ACTION = 'MY_ACTION';
const myAction = () => ({
type: MY_ACTION,
payload: {test: 'testval'},
});
const epic = action$ =>
action$.ofType(MY_ACTION).switchMap(() =>
Observable.concat(
Observable.of({type: 'test1'}),
Observable.fromPromise(Promise.resolve({type: 'test2'})),
)
);
it('it should work', () => {
const deepEquals = (actual, expected) => {
expect(actual).to.deep.equal(expected);
};
const createTestScheduler = () =>
new TestScheduler(deepEquals);
const marbles1 = '-a-';
const marbles2 = '-(bc)-';
const values = {
a: myAction(),
b: {type: 'test1'},
c: {type: 'test2'},
};
const ts = createTestScheduler();
const source = ActionsObservable.from(
ts.createColdObservable(marbles1, values)
);
const actual = epic(source);
ts.expectObservable(actual);
ts.expectObservable(actual).toBe(marbles2, values);
ts.flush();
});
...

Answer 1

Take a look at the documentation under the 'Known issues' section: https://rxjs-dev.firebaseapp.com/guide/testing/marble-testing
You can use the from operator to wrap a promise like so:
const myAsyncCode = () => from(Promise.resolve('something'));
it('has async code', (done) => {
myAsyncCode().subscribe((d) => {
assertEqual(d, 'something');
done();
});
});