This PR allows your tests to assert that a certain workflow/activity was dispatched.

Motivation behind this PR:

Assume we have the following workflow structure:

• Workflow: CreateAndLinkEntities
  • Activity: CreateEntity1 returns $entity1Id
  • Activity: CreateEntity2 returns $entity2Id
  • Activity: LinkEntity1WithEntity2 returns void
  • The workflow returns [$entity1Id, $entity2Id]

The latest release allows us to mock all three activities, but we cannot verify that the last activity has been dispatched.

With this PR you can now write:

WorkflowStub::fake();
WorkflowStub::mock(CreateEntity1::class, 1);
WorkflowStub::mock(CreateEntity2::class, 2);
WorkflowStub::mock(LinkEntity1WithEntity2::class);

$workflow = WorkflowStub::make(CreateAndLinkEntities::class);
$workflow->start();

WorkflowStub::assertDispatchedTimes(CreateEntity1::class);
WorkflowStub::assertDispatchedTimes(CreateEntity2::class);
WorkflowStub::assertDispatchedTimes(LinkEntity1WithEntity2::class);

This will also work to assert that a child workflow was dispatch.

It currently fails when we do not mock the child workflow itself, but we want to assert that the activities of the child workflow have been dispatched. We want to achieve some end-to-end-testing here.

It does not work because WithoutOverlappingMiddleware tries to get a lock on the parent workflow when trying to call the handle-Method on the child workflow.

@rmcdaniel So before finalizing this PR: What is your opinion on this issue?

1. Should it be possible to only mock child-workflows? The child workflow's activities must then be tested separately.
2. Should it be possible to not mock the child workflow and then to mock its activities?