Integrate test dispatchers with libraries using Dispatchers.Xxx

Make sure that libraries can use hard-coded withContext(Dispatchers.IO) { ... } and still be testable with test dispatchers. See also discussion in #810 and #1202.

[CharlyLafon37]

Any update on this issue ?

[wkornewald]

We do have retry handling and other code that needs to work around limitations of underlying libraries with delay and those can happen inside non-Main dispatchers. It would be really great to have the possibility to not just set the main dispatcher but really all dispatchers. Currently we still depend on a wrapper (e.g. dispatchers.io instead of Dispatchers.IO) to have full control and a well-defined test environment. Does anything speak against just providing a simple Dispatchers.setAll(dispatcher)?

Also, it would be really awesome to have some utility to make setting up coroutine-capable unit tests trivially easy. Ideally, the default behavior in unit tests would automatically switch all dispatchers and the test lib would provide a global singleton default testScope. If anyone needs more control it’s still possible to modify the default setup and use custom testScopes.

If having nice default behavior automatically is impossible, then it would be great to have something like a CoroutineTest base class or delegate or a test rule that can be added to any existing test class in as little code as possible to get the nice defaults. Anything that doesn’t require repeating that boilerplate and learning unnecessary details just to get started would be great.