Mockito Exception - when() requires an argument which has to be a method call on a mock

You need to create a MOCK of pcUserService first, and then use that mock.

PcUserService mock = org.mockito.Mockito.mock(PcUserService.class);
when(mock.read("1")).thenReturn(pcUser);

In case others hit this issue....

It could also be the case that the method you are trying to mock out,pcUserService.read, is declared as a final method. From what I've noticed this appears to cause issues with Mockito.

If you use Kotlin, you should know that methods are final by default. So write open fun instead of fun. Thanks to @djkelly99 for a tip.