Mocking

First, we will create a mock of Func.

Func mock = (Func)T.mock(Func.class);

Then we will establish the mocking method behavior. We can mock by returning a value.

T.when(mock.run(0)).thenReturn(0);
// When mock calls 'run' with 0, return 0

Or we can mock by throwing an exception.

T.when(mock.run(0)).thenThrow(new T.TestException('test'));
// When mock calls 'run' with 0, throw the exception

Or we can mock by using a Func as an answer.

T.when(mock.run(0)).thenAnswer(R.inc);
// When mock calls 'run' with 0, apply the answer Func to the arguments
// and return the result

Besides, we can use argument matcher to capture method invocation more precisely.

T.when(mock.run(T.anyBoolean(R.isNotNull))).thenReturn(0);
// When mock calls 'run' with any Boolean that is not null, return 0

Finally, let's verify the mocks.

mock.run(0);

T.verify(mock, 'run').toHaveBeenCalled();