Package org.mockito

Class ArgumentCaptor<T>

java.lang.Object
org.mockito.ArgumentCaptor<T>
public class ArgumentCaptor<T> extends Object
Use it to capture argument values for further assertions.

Mockito verifies argument values in natural java style: by using an equals() method. This is also the recommended way of matching arguments because it makes tests clean and simple. In some situations though, it is helpful to assert on certain arguments after the actual verification. For example: 


   ArgumentCaptor<Person> argument = ArgumentCaptor.forClass(Person.class);
   verify(mock).doSomething(argument.capture());
   assertEquals("John", argument.getValue().getName());
Example of capturing varargs: 

   //capturing varargs:
   ArgumentCaptor<Person> varArgs = ArgumentCaptor.forClass(Person.class);
   verify(mock).varArgMethod(varArgs.capture());
   List expected = asList(new Person("John"), new Person("Jane"));
   assertEquals(expected, varArgs.getAllValues());

Warning: it is recommended to use ArgumentCaptor with verification but not with stubbing. Using ArgumentCaptor with stubbing may decrease test readability because captor is created outside of assertion (aka verify or 'then') blocks. It may also reduce defect localization because if the stubbed method was not called, then no argument is captured.

In a way ArgumentCaptor is related to custom argument matchers (see javadoc for ArgumentMatcher class). Both techniques can be used for making sure certain arguments were passed to mock objects. However, ArgumentCaptor may be a better fit if:

  • custom argument matcher is not likely to be reused
  • you just need it to assert on argument values to complete verification
Custom argument matchers via ArgumentMatcher are usually better for stubbing.

This utility class will perform type checking on the generic type (since Mockito 5.0.0).

There is an annotation that you might find useful: @Captor

See the full documentation on Mockito in javadoc for Mockito class.

Since:
1.8.0
See Also:

  • Method Details

    • capture

      public T capture()
      Use it to capture the argument. This method must be used inside of verification.

      Internally, this method registers a special implementation of an ArgumentMatcher. This argument matcher stores the argument value so that you can use it later to perform assertions.

      See examples in javadoc for ArgumentCaptor class.

      Returns:
      null or default values

    • getValue

      public T getValue()
      Returns the captured value of the argument. When capturing varargs use getAllValues().

      If verified method was called multiple times then this method it returns the latest captured value.

      See examples in javadoc for ArgumentCaptor class.

      Returns:
      captured argument value

    • getAllValues

      public List<T> getAllValues()
      Returns all captured values. Use it when capturing varargs or when the verified method was called multiple times. When varargs method was called multiple times, this method returns merged list of all values from all invocations.

      Example: 

      
   mock.doSomething(new Person("John");
   mock.doSomething(new Person("Jane");

   ArgumentCaptor<Person> peopleCaptor = ArgumentCaptor.forClass(Person.class);
   verify(mock, times(2)).doSomething(peopleCaptor.capture());

   List<Person> capturedPeople = peopleCaptor.getAllValues();
   assertEquals("John", capturedPeople.get(0).getName());
   assertEquals("Jane", capturedPeople.get(1).getName());
      Example of capturing varargs: 
      
   mock.countPeople(new Person("John"), new Person("Jane"); //vararg method

   ArgumentCaptor<Person> peopleCaptor = ArgumentCaptor.forClass(Person.class);

   verify(mock).countPeople(peopleCaptor.capture());

   List expected = asList(new Person("John"), new Person("Jane"));
   assertEquals(expected, peopleCaptor.getAllValues());
      See more examples in javadoc for ArgumentCaptor class.
      Returns:
      captured argument value

    • forClass

      public static <U, S extends U> ArgumentCaptor<U> forClass(Class<S> clazz)
      Build a new ArgumentCaptor.

      An ArgumentCaptor will perform type checks (since Mockito 5.0.0).

      Type Parameters:
      U - Type of object captured by the newly built ArgumentCaptor
      S - Type of clazz
      Parameters:
      clazz - Type matching the parameter to be captured.
      Returns:
      A new ArgumentCaptor

    • captor

      @SafeVarargs public static <U> ArgumentCaptor<U> captor(U... reified)
      Build a new ArgumentCaptor by inferring the class type.

      This enables inferring the generic type of an argument captor without providing a raw class reference, which enables working around generic limitations of the Java compiler without producing compile-time warnings unlike forClass(java.lang.Class<S>) which would require explicit casting or warning suppression.

      Example usage: 

      
   // Given
   UserRepository repository = mock();
   UserService service = new UserService(repository);

   Map<String, User> expectedUsers = Map.of(
       "12345", new User("12345", "Bob"),
       "45678", new User("45678", "Dave")
   );

   ArgumentCaptor<Map<String, User>> captor = ArgumentCaptor.captor();

   doNothing().when(repository).storeUsers(captor.capture());

   // When
   service.createUsers(List.of(
       new User("12345", "Bob"),
       new User("45678", "Dave")
   ));

   // Then
   Map<String, User> actualUsers = captor.getValue();

   assertThat(expectedUsers).isEqualTo(actualUsers);
      Type Parameters:
      U - the type of argument to be captured by this captor.
      Parameters:
      reified - do not pass any value here. This is used to trick the compiler into reifying the return type without needing casts.
      Returns:
      A new ArgumentCaptor.
      Throws:
      IllegalArgumentException - if any arguments are passed to this method.
      Since:
      5.7.0