Stubbing Fails for Methods with Non-constant Default Parameters

Kotlin permits defining default parameters for methods that are data members of the class. However, stubbing such a method then verifying it causes a failure because stubbing will convert the default parameter to a null-value and verify assumes the default parameter is non-null. When the original type of the default parameter is non-null, there is no way for me to verify using a pattern that supports null.

To make it more concrete, I’ve attached a test case (including build script – test.tar.gz) that demonstrates the issue. Executing this test case, results in

Argument(s) are different! Wanted:
classToMock.printSomething(
    <any java.lang.String>,
    <any java.lang.String>
);
-> at ClassToMock.printSomething(Test.kt:11)
Actual invocation has different arguments:
classToMock.printSomething(
    "TEST",
    null
);
-> at ClassToMock.printSomething$default(Test.kt:10)

	at ClassToMock.printSomething(Test.kt:11)
	at DefaultParameterFail.default parameter will cause verifier failure(Test.kt:29)

Here, the stubbed method was fun printSomething(message: String, suffix: String = defaultValue). Notice that the second parameter (the default parameter) becomes null upon stubbing, so verifying that it was invoked fails.

[nhaarman]

As an alternative, you can use anyOrNull():

verify(mockedPrinter).printSomething(any(), anyOrNull())

[danielgomezrico]

@nhaarman maybe any() can check if the type is nullable and then use anyOrNull() inside of it based on that?