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Error output for completed observable

See original GitHub issue

Given code snipped produces unreadable (as expected) error output

const { merge } = require('rxjs/operators')
const { cold, hot } = require('jest-marbles');

describe("RxJS", () => {
    it('Should merge two hot observables and start emitting from the subscription point', () => {
        const e1 = hot('----a--^--b-------c--|', {a: 0});
        const e2 = hot('  ---d-^--e---------f-----|', {a: 0});
        const expected = cold('--d-(be)----c-f-----|', {a: 0});
        //                       ^--- added this so assertion fails

        expect(e1.pipe(merge(e2))).toBeObservable(expected);
    });
})

jest-marbles: 2.3.0 rxjs: 6.4.0 Output:

  ● RxJS › Should merge two hot observables and start emitting from the subscription point

    expect(received).toBeNotifications(expected)

    Expected notifications to be:
      [{"frame": 20, "notification": {"error": undefined, "hasValue": true, "kind": "N", "value": undefined}}, {"frame": 40, "notification": {"error": undefined, "hasValue": true, "kind": "N", "value": undefined}}, {"frame": 40, "notification": {"error": undefined, "hasValue": true, "kind": "N", "value": undefined}}, {"frame": 120, "notification": {"error": undefined, "hasValue": true, "kind": "N", "value": undefined}}, {"frame": 140, "notification": {"error": undefined, "hasValue": true, "kind": "N", "value": undefined}}, {"frame": 200, "notification": {"error": undefined, "hasValue": false, "kind": "C", "value": undefined}}]
    But got:
      [{"frame": 30, "notification": {"error": undefined, "hasValue": true, "kind": "N", "value": undefined}}, {"frame": 30, "notification": {"error": undefined, "hasValue": true, "kind": "N", "value": undefined}}, {"frame": 110, "notification": {"error": undefined, "hasValue": true, "kind": "N", "value": undefined}}, {"frame": 130, "notification": {"error": undefined, "hasValue": true, "kind": "N", "value": undefined}}, {"frame": 190, "notification": {"error": undefined, "hasValue": false, "kind": "C", "value": undefined}}]

    Difference:

    - Expected
    + Received

      Array [
        Object {
    -     "frame": 20,
    +     "frame": 30,
          "notification": Notification {
            "error": undefined,
            "hasValue": true,
            "kind": "N",
            "value": undefined,
          },
        },
        Object {
    -     "frame": 40,
    +     "frame": 30,
          "notification": Notification {
            "error": undefined,
            "hasValue": true,
            "kind": "N",
            "value": undefined,
          },
        },
        Object {
    -     "frame": 40,
    +     "frame": 110,
          "notification": Notification {
            "error": undefined,
            "hasValue": true,
            "kind": "N",
            "value": undefined,
          },
        },
        Object {
    -     "frame": 120,
    +     "frame": 130,
          "notification": Notification {
            "error": undefined,
            "hasValue": true,
            "kind": "N",
            "value": undefined,
          },
        },
        Object {
    -     "frame": 140,
    +     "frame": 190,
          "notification": Notification {
            "error": undefined,
    -       "hasValue": true,
    -       "kind": "N",
    -       "value": undefined,
    -     },
    -   },
    -   Object {
    -     "frame": 200,
    -     "notification": Notification {
    -       "error": undefined,
            "hasValue": false,
            "kind": "C",
            "value": undefined,
          },
        },
      ]

      at TestScheduler.assertDeepEqual (node_modules/jest-marbles/umd/webpack:/JestMarbles/src/rxjs/assert-deep-equal.ts:29:20)
      at Object.<anonymous> (node_modules/jest-marbles/umd/webpack:/JestMarbles/index.ts:67:19)

Looks like a root cause of the issue is in this line https://github.com/meltedspark/jest-marbles/blob/29360098dea0ea95d7b714c75d1be0d5de8a4b15/src/jest/custom-matchers.ts#L13 Completion notification produces undefined value which fails check in containNonCharacterValue function.