Mocking a function with matchers that has default arguments throws InvalidUseOfMatchersException

class UnderTest {
  fun doStuff(string1: String, string2: String = "hello world") = "do stuff"
}

@Test
fun testIt() {
  val underTest = mock(UnderTest::class.java)
  whenever(underTest.doStuff(anyString())).thenReturn("stuff done")
}

InvalidUseOfMatchersException “This exception may occur if matchers are combined with raw values”

Theoretically adding @JvmOverloads to doStuff should fix it but it didn’t. Even if it did, it would be nice if mockito-kotlin could figure out how to generate a matcher that matches the default value. Alternatively, automatically generate an any() matcher.

[zwieback]

To solve this issue you can try the following code:

class UnderTest {
  fun doStuff(string1: String, string2: String) = "do stuff"
  fun doStuff(string1: String) = doStuff(string1, "hello world")
}

I know it’s not the true Kotlin way, but it’s only a workaround.

[guelo]

I wonder if it would be possible to use the advanced Mockito APIs to intercept the call and add the extra matchers automatically. https://static.javadoc.io/org.mockito/mockito-core/2.23.4/org/mockito/Mockito.html#framework_integrations_api