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At a glance

1. 1Matchers: when(repo.find(anyLong())).thenReturn(order)If one argument uses a matcher, all must: eq("a") for the literal ones.
2. 2Verification: verify(mailer, times(1)).send(any()), never(), atLeastOnce(), verifyNoMoreInteractions(mailer), and InOrder inOrder = inOrder(a, b); inOrder.verify(a).x(); inOrder.verify(b).y();
3. 3Stubbing side effects and errors: doThrow(new IOException()).when(out).write(any()) works also for void methods; thenAnswer(inv -> inv.getArgument(0)) returns the input
4. 4ArgumentCaptor<Order> captor = ArgumentCaptor.forClass(Order.class); verify(repo).save(captor.capture()); then assert on captor.getValue()
5. 5spy(realObject) calls real methods unless stubbed; use doReturn(x).when(spy).m() so the real method is not called while stubbingmockStatic (with try-with-resources) fakes static methods.

• Mock the collaborators at your boundaries (repositories, HTTP clients), not value objects, and not the class under test
• Strict stubs (default with the Mockito extension) fail on unused stubbings, which cleans up tests
• Mockito creates a subclass (or uses an inline mock maker with instrumentation for finals and statics) whose methods record the invocation and look up a stubbed answer in the mock's handler

import static org.mockito.Mockito.*;import static org.mockito.ArgumentMatchers.*;import org.mockito.ArgumentCaptor;class Notifier {  interface Mailer { void send(String to, String body); }  interface Users { String emailOf(long id); }  static void notifyUser(Users users, Mailer mailer, long id) { mailer.send(users.emailOf(id), "hi"); }  static void check() {    Users users = mock(Users.class);    Mailer mailer = mock(Mailer.class);    when(users.emailOf(anyLong())).thenReturn("a@x.org");    notifyUser(users, mailer, 7L);    ArgumentCaptor<String> to = ArgumentCaptor.forClass(String.class);    verify(mailer, times(1)).send(to.capture(), eq("hi"));    verifyNoMoreInteractions(mailer);  }}

1. line 2 uses ArgumentMatchers, the core of Mockito: matchers, verification, spies
2. line 11 uses any, the core of Mockito: matchers, verification, spies
3. line 14 uses times, the core of Mockito: matchers, verification, spies
4. line 15 uses verifyNoMoreInteractions, the core of Mockito: matchers, verification, spies

How Unravel recognises it

When you paste code, Unravel looks for these signs of mockito: matchers, verification, spies. Spotting them yourself is a good habit when you read unfamiliar code:

• Types: ArgumentMatchers InOrder BDDMockito
• Method calls: any() anyString() anyInt() anyLong() eq() times() never() atLeast() atLeastOnce() inOrder() doReturn() doThrow() doNothing() verifyNoInteractions() and 8 more

Part of a learning path

• Errors, logging and tests in depth · previous: AssertJ fluent assertions · next: JUnit 4 and Hamcrest

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