This stub is wrong :
doNothing().when(mockObject.methodToStub(captor.capture())); // wrong
methodToStub(...) must be outside the when if using this API style (it should only contain the mock) :
doNothing().when(mockObject).methodToStub(captor.capture()); // correct
Tho remarks however :
doNothingis the default for void methods for a mock.- You can use the
BDDMockitoaliases that enables your code to be real à la Behavior Driven Development