mockk | mocking library for Kotlin | Mock library

You can test exceptions using assertThrows:

If you want to verify that your method was not called, you can verify that it was called exactly 0 times:

You can use answers instead of returns and have a plethora of options to return something depending on the input, e.g.

as @Demigod indicated, add line unitTests.returnDefaultValues = true into your module build.gradle:

Are you sure it fails because it attempts to call the creteFinalObject function? Because when reading your code, I think that should be impossible (of course, never say never :D). The creteFinalObject function can only be called if both object1.await() and object2.await() return successfully.

I think something else is going on. Because you're doing 2 separate async tasks (getting object 1 and getting object 2), I suspect that the ordering of these 2 tasks would result in either a success or a failure.

Running your code locally, I notice that it sometimes fails at this line:

verify(atMost = 1) { bringObject2FromSomewhere() }

And I think there is your error. If bringObject1FromSomewhere() is called before bringObject2FromSomewhere(), the exception is thrown and the second function invocation never happens, causing the test to fail. The other way around (2 before 1) would make the test succeed. The Dispatchers.Default uses an internal work queue, where jobs that are cancelled before they are even started will never start at all. And the first task can fail fast enough for the second task to not being able to start at all.

I thought the fix would be to use verify(atLeast = 0, atMost = 1) { bringObject2FromSomewhere() } instead, but as I see on the MockK GitHub issues page, this is not supported (yet): https://github.com/mockk/mockk/issues/806

So even though you specify that bringObject2FromSomewhere() should be called at most 1 time, it still tries to verify it is also called at least 1 time, which is not the case.

You can verify this by adding a delay to the async call to get the first object:

After many tries, I cannot do this easily without expecting strange behaviors. So I refactored my function to use a Channel and a CoroutineScope separately. Thanks to the CoroutineScope plus extension, I can create a new scope from the flow builder. This is now testable!

Therefore, the flow builder became:

Here's how to do it in mockk (I highly recommend switching away from Mockito, mockk is just so much easier):

First thing:

getMyData is NOT a suspend function so probably you should NOT be using coEvery when mocking it (tho I'm not a Mockk user).

That being said, Retrofit does support suspend functions natively, so you could do:

You can try to use JUnit Jupiter library, it allows to test throwing Exceptions by using assertThrows method. For example if you want to test that service.getAddress() function throws some Exception under certain conditions you can test it like the following: