How to use ArgumentCaptor for stubbing

Question

In Mockito documentation and javadocs it says      It is recommended to use ArgumentCaptor with verification but not with stubbing    but I don t understand how ArgumentCaptor can be used for stubbing  Can someone explain the above statement and show how ArgumentCaptor can be used for stubbing or provide a link that shows how it can be done

User · Accepted Answer

Assuming the following method to test   public boolean doSomething SomeClass arg     Mockito documentation says that you should not use captor in this way    when someObject doSomething argumentCaptor capture     thenReturn true   assertThat argumentCaptor getValue    equalTo expected      Because you can just use matcher during stubbing   when someObject doSomething eq expected    thenReturn true     But verification is a different story  If your test needs to ensure that this method was called with a specific argument  use ArgumentCaptor and this is the case for which it is designed   ArgumentCaptor lt SomeClass gt  argumentCaptor   ArgumentCaptor forClass SomeClass class   verify someObject  doSomething argumentCaptor capture     assertThat argumentCaptor getValue    equalTo expected

User · Answer

Hypothetically  if search landed you on this question then you probably want this   doReturn someReturn  when someObject  doSomething argThat argument - gt  argument getName   equals  Bob        Why  Because like me you value time and you are not going to implement  equals just for the sake of the single test scenario   And 99   of tests fall apart with null returned from Mock and in a reasonable design you would avoid return null at all costs  use Optional or move to Kotlin  This implies that verify does not need to be used that often and ArgumentCaptors are just too tedious to write

User · Answer

The line when someObject doSomething argumentCaptor capture     thenReturn true    would do the same as when someObject doSomething Matchers any     thenReturn true    So  using argumentCaptor capture   when stubbing has no added value  Using Matchers any   shows better what really happens and therefor is better for readability  With argumentCaptor capture    you can t read what arguments are really matched  And instead of using any    you can use more specific matchers when you have more information  class of the expected argument   to improve your test  And another problem  If using argumentCaptor capture   when stubbing it becomes unclear how many values you should expect to be captured after verification  We want to capture a value during verification  not during stubbing because at that point there is no value to capture yet  So what does the argument captors capture method capture during stubbing  It capture anything because there is nothing to be captured yet  I consider it to be undefined behavior and I don t want to use undefined behavior

[java] How to use ArgumentCaptor for stubbing?

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