How to use ArgumentCaptor for stubbing?

java unit-testing junit mockito
Can't Tell picture Can't Tell · Sep 6, 2012 · Viewed 148.2k times · Source

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?

Answer

Rorick picture Rorick · Sep 6, 2012

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<SomeClass> argumentCaptor = ArgumentCaptor.forClass(SomeClass.class);
verify(someObject).doSomething(argumentCaptor.capture());
assertThat(argumentCaptor.getValue(), equalTo(expected));

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