How to use the single-spa.triggerAppChange function in single-spa

it(`is never bootstrapped`, () => {
    return singleSpa
      .triggerAppChange()
      .then(() => {
        expect(myApp.isBootstrapped()).toEqual(false);
        expect(singleSpa.getMountedApps()).toEqual([]);
        expect(singleSpa.getAppStatus('./invalid-no-mount.app.js')).toEqual('SKIP_BECAUSE_BROKEN');
      })
  });

it(`goes through the whole lifecycle successfully`, () => {
    expect(myApp.isMounted()).toEqual(false);
    expect(singleSpa.getMountedApps()).toEqual([]);

    location.hash = 'happy-basic';

    return singleSpa
      .triggerAppChange()
      .then(() => {
        expect(myApp.wasBootstrapped()).toEqual(true);
        expect(myApp.isMounted()).toEqual(true);
        expect(singleSpa.getMountedApps()).toEqual(['./happy-basic.app.js']);

        location.hash = '#not-happy-basic';

        return singleSpa
          .triggerAppChange()
          .then(() => {
            expect(myApp.wasBootstrapped()).toEqual(true);
            expect(myApp.isMounted()).toEqual(false);
            expect(singleSpa.getMountedApps()).toEqual([]);
          })
      })

it(`is bootstrapped and mounted, but then put in a broken state`, () => {
    location.hash = activeHash;

    return singleSpa
      .triggerAppChange()
      .then(() => {
        expect(myApp.wasBootstrapped()).toEqual(true);
        expect(myApp.wasMounted()).toEqual(true);
        expect(singleSpa.getMountedApps()).toEqual([]);
        expect(singleSpa.getAppStatus('./invalid-mount.app.js')).toEqual('SKIP_BECAUSE_BROKEN');

        location.hash = 'not-invalid-mount';

        return singleSpa
          .triggerAppChange()
          .then(() => {
            expect(singleSpa.getMountedApps()).toEqual([]);
            expect(singleSpa.getAppStatus('./invalid-mount.app.js')).toEqual('SKIP_BECAUSE_BROKEN');
          })
      })

it(`goes through the whole lifecycle successfully`, () => {
    expect(myApp.wasMounted()).toEqual(false);
    expect(singleSpa.getMountedApps()).toEqual([]);

    location.hash = '#returns-non-native-promise';

    return singleSpa
      .triggerAppChange()
      .then(() => {
        expect(myApp.wasBootstrapped()).toEqual(true);
        expect(myApp.wasMounted()).toEqual(true);
        expect(singleSpa.getMountedApps()).toEqual(['./returns-non-native-promise.app.js']);

        location.hash = '#something-else';

        return singleSpa
          .triggerAppChange()
          .then(() => {
            expect(myApp.wasBootstrapped()).toEqual(true);
            expect(myApp.wasUnmounted()).toEqual(true);
            expect(singleSpa.getMountedApps()).toEqual([]);
          })
      })

it(`should throw an error when mounting fails`, () => {
        const app = createApp();
        let shouldAppBeMounted = true;

        singleSpa.registerApplication('parcel-bootstrap-errors', app, () => shouldAppBeMounted);
        return singleSpa.triggerAppChange().then(() => {
          expect(app.mountCalls).toBe(1)

          const parcelConfig1 = createParcelConfig('bootstrap')
          parcelConfig1.name = 'bootstrap-error'
          const parcel1 = app.mountProps.mountParcel(parcelConfig1, {domElement: document.createElement('div')})
          return parcel1.bootstrapPromise.catch(err => {
            expect(err.name).toBe('bootstrap-error');
            expect(err.message.indexOf(`SKIP_BECAUSE_BROKEN`)).toBeGreaterThan(-1);
            expect(err.message.indexOf(`bootstrap-error`)).toBeGreaterThan(-1);
          }).then(() => {
            expect(parcel1.getStatus()).toBe('SKIP_BECAUSE_BROKEN')
          })
        })
      })

it(`bootstraps and mounts, but then is put into SKIP_BECAUSE_BROKEN once it unmounts`, () => {
    location.hash = activeHash;

    return singleSpa
      .triggerAppChange()
      .then(() => {
        expect(myApp.numBootstraps()).toEqual(1);
        expect(myApp.numMounts()).toEqual(1);
        expect(myApp.numUnmounts()).toEqual(0);
        expect(singleSpa.getMountedApps()).toEqual(['./unmount-rejects.app.js']);
        expect(singleSpa.getAppStatus('./unmount-rejects.app.js')).toEqual('MOUNTED');

        location.hash = '#not-unmount-rejects';

        return singleSpa
          .triggerAppChange()
          .then(() => {
            expect(myApp.numUnmounts()).toEqual(1);
            expect(singleSpa.getMountedApps()).toEqual([]);
            expect(singleSpa.getAppStatus('./unmount-rejects.app.js')).toEqual('SKIP_BECAUSE_BROKEN');

it(`unloads an app that is mounted, and then remounts it`, () => {
      location.hash = activeHash;

      return singleSpa
        .triggerAppChange()
        .then(() => {
          expect(singleSpa.getAppStatus('./happy-unload.app.js')).toEqual('MOUNTED');
          expect(myApp.getNumBootstrapCalls()).toBe(1);
          expect(myApp.getNumMountCalls()).toBe(1);
          expect(myApp.getNumUnmountCalls()).toBe(0);
          expect(myApp.getNumUnloadCalls()).toBe(0);
          location.hash = '#';
          return singleSpa.unloadApplication('./happy-unload.app.js');
        })
        .then(() => {
          expect(singleSpa.getAppStatus('./happy-unload.app.js')).toEqual('NOT_LOADED');
          expect(myApp.getNumBootstrapCalls()).toBe(1);
          expect(myApp.getNumMountCalls()).toBe(1);
          expect(myApp.getNumUnmountCalls()).toBe(1);
          expect(myApp.getNumUnloadCalls()).toBe(1);

it(`is just waited for if dieOnTimeout is false`, () => {
    location.hash = '#bootstrap-times-out';

    return singleSpa
      .triggerAppChange()
      .then(() => {
        expect(myApp.wasBootstrapped()).toEqual(true);
        expect(myApp.wasMounted()).toEqual(true);
        expect(singleSpa.getMountedApps()).toEqual(['./bootstrap-times-out.app.js']);
        expect(singleSpa.getAppStatus('./bootstrap-times-out.app.js')).toEqual(singleSpa.MOUNTED);
        expect(errs.length).toBe(0);
      })
  });
});

parcelConfig = createParcelConfig();

    shouldAppBeMounted = true;

    expect(app.bootstrapCalls).toBe(0);
    expect(app.mountCalls).toBe(0);
    expect(app.unmountCalls).toBe(0);

    expect(parcelConfig.bootstrapCalls).toBe(0);
    expect(parcelConfig.mountCalls).toBe(0);
    expect(parcelConfig.unmountCalls).toBe(0);

    let parcel, unmountPromiseHasResolved = false;

    return singleSpa
      .triggerAppChange()
      .then(() => {
        expect(app.bootstrapCalls).toBe(1);
        expect(app.mountCalls).toBe(1);
        expect(app.unmountCalls).toBe(0);

        parcel = app.mountProps.mountParcel(parcelConfig, {domElement: document.createElement('div')});

        parcel.unmountPromise
          .then(() => unmountPromiseHasResolved = true)

        expect(parcel.getStatus()).toBe(singleSpa.NOT_BOOTSTRAPPED);
        expect(unmountPromiseHasResolved).toBe(false);

        return parcel
          .bootstrapPromise

.then(() => {
        expect(bootstrapped).toEqual(true);
        expect(mounted).toEqual(true);
        expect(singleSpa.getMountedApps()).toEqual(['register-with-object']);

        location.hash = '#not-register-with-object';

        return singleSpa
          .triggerAppChange()
          .then(() => {
            expect(bootstrapped).toEqual(true);
            expect(mounted).toEqual(false);
            expect(singleSpa.getMountedApps()).toEqual([]);
          })
      })
  });