Mocking the e-mail server

Again, the library application has a field representing the E-mail server, which is then mocked by an MockEmailServerHolder. However, in this case, we don't have to fake the result of sendEmail (which does not exists because it is void method), we are interested if we are actually calling the sendEmail method. To this end, we use the method verify imported as "import static org.mockito.Mockito.verify;". Verfiy allows us to check that a message has been sent. For example, if aLibraryApp.sendReminder() is supposed to send the message "sendEmail("user@domain","Overdue book(s)","You have 1 overdue book(s)")", then

verify(mockEmailServer).sendEmail("user@domain", "Overdue book(s)", "You have 1 overdue book(s)");