Utilities for easily running tests against streams of arrays of arrays of streams of streams of... you get the idea. (most.js + mocha + chai)

example-test.js

it('projectStaticsToArrayOfPairStreams() should return an array of streams of key/state objects', () => {
  const statics = internals.projectStaticsToArrayOfPairStreams(partitioned.statics);
  return deepCapture(statics)
    .then(result => {
      const expected = [
        $([{ key: 'a', state: { x: 1, y: 2 } }, { key: 'a', state: { x: 3, y: 4 } }]),
        $([{ key: 'b', state: { x: 5, y: 6 } }, { key: 'b', state: { x: 7, y: 8 } }]),
        $([{ key: 'c', state: { } }])
      ];
      assert.deepEqual(expected, result);
    });
});

it('projectStreamsToArrayOfStreamsOfPairStreams() should return an array of nested streams of key/state pairs', () => {
  const pair$$arr = internals.projectStreamsToArrayOfStreamsOfPairStreams(partitioned.streams);
  return deepCapture(pair$$arr)
    .then(result => {
      const expected = [
        $([
          $([{ key: 'd', state: {x:10, y:11}}, { key: 'd', state: { x:12, y:13 }}]),
          $([{ key: 'd', state: {x:14, y:15}}, { key: 'd', state: { x:16, y:17 }}])
        ]),
        $([
          $([{ key: 'e', state: { y: 18 } }])
        ])
      ];
      assert.deepEqual(expected, result);
    });
});

test-utils.js

const run = fn => new Promise(resolve => resolve(fn()));
const $ = arr => ((arr.isStream = true), arr);

function deepCapture(source) {
  return run(() => {
    if(source instanceof Array) return Promise.all(source.map(deepCapture));
    if(source instanceof most.Stream) return source
       .reduce((acc, x) => (acc.push(Promise.resolve(deepCapture(x))), acc), [])
       .then(arr => Promise.all(arr).then($));
    return source;
  });
}