Class ArgumentMatcher<T>

  extended by org.hamcrest.BaseMatcher<T>
      extended by org.mockito.ArgumentMatcher<T>
Type Parameters:
T - type of argument
All Implemented Interfaces:
org.hamcrest.Matcher<T>, org.hamcrest.SelfDescribing
Direct Known Subclasses:
And, Any, AnyVararg, CapturingMatcher, CompareTo, Contains, EndsWith, Equals, EqualsWithDelta, Find, InstanceOf, Matches, Not, NotNull, Null, Or, ReflectionEquals, Same, StartsWith

public abstract class ArgumentMatcher<T>
extends org.hamcrest.BaseMatcher<T>

Allows creating customized argument matchers.

ArgumentMatcher is an hamcrest Matcher with predefined describeTo() method. In case of failure, ArgumentMatcher generates description based on decamelized class name - to promote meaningful class names. For example StringWithStrongLanguage matcher will generate 'String with strong language' description. You can always override describeTo() method and provide detailed description.

Use Matchers.argThat(org.hamcrest.Matcher) method and pass an instance of hamcrest Matcher, e.g:

 class IsListOfTwoElements extends ArgumentMatcher<List> {
     public boolean matches(Object list) {
         return ((List) list).size() == 2;
 List mock = mock(List.class);
 when(mock.addAll(argThat(new IsListOfTwoElements()))).thenReturn(true);
 mock.addAll(Arrays.asList("one", "two"));
 verify(mock).addAll(argThat(new IsListOfTwoElements()));
To keep it readable you may want to extract method, e.g:
   verify(mock).addAll(argThat(new IsListOfTwoElements()));
Warning: Be reasonable with using complicated argument matching, especially custom argument matchers, as it can make the test less readable. Sometimes it's better to implement equals() for arguments that are passed to mocks (Mockito naturally uses equals() for argument matching). This can make the test cleaner.

Also, sometimes ArgumentCaptor may be a better fit than custom matcher. For example, if custom argument matcher is not likely to be reused or you just need it to assert on argument values to complete verification of behavior.

Read more about other matchers in javadoc for Matchers class

Constructor Summary
Method Summary
 void describeTo(org.hamcrest.Description description)
abstract  boolean matches(java.lang.Object argument)
          Returns whether this matcher accepts the given argument.
Methods inherited from class org.hamcrest.BaseMatcher
_dont_implement_Matcher___instead_extend_BaseMatcher_, toString
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail


public ArgumentMatcher()
Method Detail


public abstract boolean matches(java.lang.Object argument)
Returns whether this matcher accepts the given argument.

The method should never assert if the argument doesn't match. It should only return false.

argument - the argument
whether this matcher accepts the given argument.


public void describeTo(org.hamcrest.Description description)