mainDispatcher
Returns a test configuration which specifies a main dispatcher (Dispatchers.setMain) for a TestElement hierarchy.
If dispatcher is null, a single-threaded dispatcher is used.
Note: Only one main dispatcher may exist at any point in time. Therefore, – this configuration may not be overridden at lower levels of the TestElement hierarchy, and
multiple TestElement hierarchys with a mainDispatcher configuration may not execute concurrently. Child elements inherit the main dispatcher as part of their CoroutineContext.