How to use systemClassLoader method of org.mockitoutil.ClassLoaders class

You can do it either:

with @SuppressWarnings("unchecked")

  @Test
  @SuppressWarnings("unchecked")
  void TestDoSomething(){
    SubClass sb = mock(SubClass.class);

    Example ex = new Example(sb);

    ArgumentCaptor<Map<String, CompoundClass>> argCaptor = ArgumentCaptor.forClass(Map.class);

    ex.doSomeThing();

    verify(sb).doSomeThingSubClass(argCaptor.capture());

    System.out.println(argCaptor.getValue().get("x").a);
  }

or with junit5 and @Captor annotation:

import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.verify;

import java.util.HashMap;
import java.util.Map;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestInstance;
import org.junit.jupiter.api.TestInstance.Lifecycle;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.ArgumentCaptor;
import org.mockito.Captor;
import org.mockito.junit.jupiter.MockitoExtension;

@ExtendWith(MockitoExtension.class)
@TestInstance(Lifecycle.PER_METHOD)
public class TestDoSomething {

  @Captor
  private ArgumentCaptor<Map<String, CompoundClass>> argCaptor;

  @Test
  void TestDoSomething2(){
    SubClass sb = mock(SubClass.class);

    Example ex = new Example(sb);

    ex.doSomeThing();

    verify(sb).doSomeThingSubClass(argCaptor.capture());

    System.out.println(argCaptor.getValue().get("x").a);
  }
}

For Java 8 and above, it's easy:

when(mock.process(Matchers.anyList()));

For Java 7 and below, the compiler needs a bit of help. Use anyListOf(Class<T> clazz):

when(mock.process(Matchers.anyListOf(Bar.class)));

To see coverage for production code change the pattern to com.cdk.dmg.asset.

You need to Enable coverage in test folders if you want see coverage in tests (this option is disabled on your screenshot and the pattern is set to record data for tests only, hence no results).

Declare the exception in the test method.

public void testAddUser() throws ServiceException {
...
}

When you want to use the @Mock annotation you should use the MockitoJUnitRunner

@RunWith(MockitoJUnitRunner.class)
public class MockitoTest {

    @Mock
    private IRoutingObjHttpClient routingClientMock;

    @Test
    public void testSendRoutingRequest() throws Exception {
        // ...
    }

}

See also this tutorial.

I think you do need to cast it, but it shouldn't be too bad:

Foo<Bar> mockFoo = (Foo<Bar>) mock(Foo.class);
when(mockFoo.getValue()).thenReturn(new Bar());

If I were you, I would simply mock the services A and B and your executors, then inject them thanks to the annotation @InjectMocks as they are fields of your class.

If you want mock the method execute of your Executor, you should rather proceed as next to simply call the method run of the provided Runnable:

doAnswer(
    (InvocationOnMock invocation) -> {
        ((Runnable) invocation.getArguments()[0]).run();
        return null;
    }
).when(serviceAExecutorService).execute(any(Runnable.class));

So basically your test would be something like this:

@RunWith(MockitoJUnitRunner.class)
public class CompletableFutureServiceTest {

    // The mock of my service A
    @Mock
    private ServiceA ServiceA;
    // The mock of my service B
    @Mock
    private ServiceB ServiceB;
    // The mock of your executor for the service A
    @Mock
    private Executor serviceAExecutorService;
    // The mock of your executor for the service B
    @Mock
    private Executor serviceBExecutorService;
    // My class in which I want to inject the mocks
    @InjectMocks
    private CompletableFutureService service;

    @Test
    public void testSomeMethod() {
        // Mock the method execute to call the run method of the provided Runnable
        doAnswer(
            (InvocationOnMock invocation) -> {
                ((Runnable) invocation.getArguments()[0]).run();
                return null;
            }
        ).when(serviceAExecutorService).execute(any(Runnable.class));
        doAnswer(
            (InvocationOnMock invocation) -> {
                ((Runnable) invocation.getArguments()[0]).run();
                return null;
            }
        ).when(serviceBExecutorService).execute(any(Runnable.class));

        ServiceAResponse serviceAResponse = ... // The answer to return by service A
        // Make the mock of my service A return my answer
        when(ServiceA.retrieve(any(ServiceARequest.class))).thenReturn(
            serviceAResponse
        );
        ServiceBResponse serviceBResponse = ... // The answer to return by service B
        // Make the mock of my service B return my answer
        when(ServiceB.retrieve(any(ServiceBRequest.class))).thenReturn(
            serviceBResponse
        );

        // Execute my method
        ServiceResponse response = service.someMethod(
            new ServiceARequest(), new ServiceBRequest()
        );

        // Test the result assuming that both responses are wrapped into a POJO
        Assert.assertEquals(serviceAResponse, response.getServiceAResponse());
        Assert.assertEquals(serviceBResponse, response.getServiceBResponse());
    }
}

In general mocking static calls is the last resort, that is not supposed to be used as default approach.

For example, for testing the code, that works with file system, there are better means. E.g. depending on the junit version either use TemporaryFolder rule or @TempDir annotation.

Also, please note, that Mockito.mockStatic might significantly slow down your tests (e.g. look at the notes below).

Having said the caution above, find the snippet below, that shows how to test, that file got removed.

class FileRemover {
    public static void deleteFile(Path filePath) throws IOException {
        Files.delete(filePath);
    }
}

class FileRemoverTest {

    @TempDir
    Path directory;

    @Test
    void fileIsRemovedWithTemporaryDirectory() throws IOException {
        Path fileToDelete = directory.resolve("fileToDelete");
        Files.createFile(fileToDelete);

        FileRemover.deleteFile(fileToDelete);

        assertFalse(Files.exists(fileToDelete));
    }

    @Test
    void fileIsRemovedWithMockStatic() throws IOException {
        Path fileToDelete = Paths.get("fileToDelete");
        try (MockedStatic<Files> removerMock = Mockito.mockStatic(Files.class)) {
            removerMock.when(() -> Files.delete(fileToDelete)).thenAnswer((Answer<Void>) invocation -> null);
            // alternatively
            // removerMock.when(() -> Files.delete(fileToDelete)).thenAnswer(Answers.RETURNS_DEFAULTS);

            FileRemover.deleteFile(fileToDelete);

            removerMock.verify(() -> Files.delete(fileToDelete));
        }
    }
}

Notes:

1. Mockito.mockStatic is available in Mockito 3.4 and above, so check you're using correct version.

2. The snippet deliberatly shows two approaches: @TempDir and Mockito.mockStatic. When run both tests you'll notice that Mockito.mockStatic is much slower. E.g. on my system test with Mockito.mockStatic runs around 900 msec vs 10 msec for @TempDir.

In my case, I had a similar issue when I worked with JUnit5

@ExtendWith(MockitoExtension.class)
class MyServiceTest {
...

@InjectMocks
MyService underTest;

@Test
void myMethodTest() {
...
}

underTest was null. The cause of the problem was that I used @Test from JUnit4 package import org.junit.Test; instead JUnit5 import org.junit.jupiter.api.Test;