argThat plus lambda

that is how you can fail your argument verification:

    verify(mock).mymethod(argThat(
                            x -> false ));

where

import static org.mockito.ArgumentMatchers.argThat;
import static org.mockito.Mockito.verify;

argThat plus asserts

the above test will "say" Expected: lambda$... Was: YourClass.toSting.... You can get a more specific cause of the failure if to use asserts in the the lambda:

    verify(mock).mymethod(argThat( x -> {
      assertThat(x).isNotNull();
      assertThat(x.description).contains("KEY");
      return true;
    }));

❗️BUT❗️: THIS ONLY WORKS WHEN

• THE CALL IS EXPECTED 1 TIME, or
• the call is expected 2+ times, but all the times the verifier matches (returns true).

If the verified method called 2+ times, mockito passes all the called combinations to each verifier. So mockito expects your verifier silently returns true for one of the argument set, and false (no assert exceptions) for other valid calls. That expectation is not a problem for 1 method call - it should just return true 1 time.

import static org.assertj.core.api.Assertions.assertThat;
import static org.mockito.ArgumentMatchers.argThat;
import static org.mockito.Mockito.verify;

Now the failed test will say: Expected: Obj.description to contain 'KEY'. Was: 'Actual description'. NOTE: I used assertJ asserts, but it's up to you which assertion framework to use.

direct argument

Mokito compares direct arguments using equals():

verify(mock).mymethod(expectedArg);
// NOTE:   ^ where the parentheses must be closed.

eq matcher

• Never use eq for a single arg. Use the aforementioned direct argument.
• Mokito compares direct arguments using equals()
• Reason: eq would be a SonarQube / SonarClound violation: https://rules.sonarsource.com/java/tag/mockito/RSPEC-6068

argThat with multiple arguments.

If you use argThat, all arguments must be provided with matches. E.g. if, in a different case, you had another method with 2 arguments:

    verify(mock).mymethod2(eq("VALUE_1"), argThat((x)->false));
    // above is correct as eq() is also an argument matcher.

verify(mock).mymethod2("VALUE_1", argThat((x)->false));

// above is incorrect; an exception will be thrown, as the first arg. is given without an argument matcher.

where:

import static org.mockito.ArgumentMatchers.argThat;
import static org.mockito.ArgumentMatchers.eq;
import static org.mockito.Mockito.verify;

THE ROOT CAUSE of original question failure was the wrong place of the parentheses:

• verify(mock.mymethod.... That was wrong. The right would be:
• verify(mock).*

I have used Mockito.verify in this way

@UnitTest
public class JUnitServiceTest
{
    @Mock
    private MyCustomService myCustomService;


    @Test
    public void testVerifyMethod()
    {
       Mockito.verify(myCustomService, Mockito.never()).mymethod(parameters); // method will never call (an alternative can be pick to use times(0))
       Mockito.verify(myCustomService, Mockito.times(2)).mymethod(parameters); // method will call for 2 times
       Mockito.verify(myCustomService, Mockito.atLeastOnce()).mymethod(parameters); // method will call atleast 1 time
       Mockito.verify(myCustomService, Mockito.atLeast(2)).mymethod(parameters); // method will call atleast 2 times
       Mockito.verify(myCustomService, Mockito.atMost(3)).mymethod(parameters); // method will call at most 3 times
       Mockito.verify(myCustomService, Mockito.only()).mymethod(parameters); //   no other method called except this
    }
}

Many of the above answers confused me but I suspect it may be due to older versions of Mockito. This answer is accomplished using

• Java 11
• Mockito 3.1.0
• SpringBoot 2.2.7.RELEASE
• JUnit5

Using ArgumentCaptor I have done it this way:

@Mock
MyClientService myClientService;
@InjectMocks 
MyService myService;


@Test
void myTest() {

  ArgumentCaptor<String> captorParam1 = ArgumentCaptor.forClass(String.class);
  ArgumentCaptor<String> captorParam2 = ArgumentCaptor.forClass(String.class);

  Mockito.when(myClientService.doSomething(captorParam1.capture(), captorParam2.capture(), ArgumentMatchers.anyString()))
      .thenReturn(expectedResponse);

  assertDoesNotThrow(() -> myService.process(data));

  assertEquals("param1", captorParam1.getValue());
  assertEquals("param2", captorParam2.getValue());

  verify(myClientService, times(1))
    .doSomething(anyString(), anyString(), anyString());
}

Verify(a).aFunc(eq(b))

In pseudocode:

When in the instance a - a function named aFunc is called.

Verify this call got an argument which is equal to b.