Mockito, argThat, and hasEntry

Question

tl;dr: These tests don't compile because the type parameters don't match. What changes should I make to make them compile and run correctly?

https://github.com/wesleym/matchertest

I have some non-test code that calls into a service. It calls the service's activate method with a map parameter.

public class Foo {
  private final Service service;

  public Foo(Service service) {
    this.service = service;
  }

  public void bar() {
    Map<String, ?> params = getParams();
    service.activate(params);
  }

  private Map<String, ?> getParams() {
    // something interesting goes here
  }
}

Some code I'm trying to test has a dependency on a service like this one:

public interface Service {
  public void activate(Map<String, ?> params);
}

I'd like to test this code by mocking the service with Mockito and verifying that activate was called with a reasonable map. The following code works:

@Test
public void testExactMap() {
  Service mockService = mock(Service.class);
  Foo foo = new Foo(mockService);

  foo.bar();

  Map<String, String> expectedParams = new HashMap<>();
  expectedParams.put("paramName", "paramValue");
  verify(service).activate(expectedParams);
}

However, I'd like to just test that the map contains one particular entry. The Hamcrest hasEntry matcher seems perfect for this use case:

@Test
public void testHasEntry() {
    Service mockService = mock(Service.class);
    Foo foo = new Foo(mockService);

    foo.bar();

    verify(mockService).activate(argThat(hasEntry("paramName", "paramValue")));
}

When I try this, I get the following error in IntelliJ IDEA:

Error:(31, 45) java: incompatible types: inference variable T has incompatible bounds
    equality constraints: java.util.Map<? extends java.lang.String,? extends java.lang.String>
    upper bounds: java.util.Map<java.lang.String,?>,java.lang.Object

The problem here is that I need a Mockito matcher of Map<String, ?>, but hasEntry gives me a matcher of Map<? extends String, ? extends String>. Even with explicit type parameters, I can't figure out what to do to reconcile the "? extends" part of the type parameter. What should I do to resolve this error? Is there a specific cast or explicit type parameter I should use?

I understand that I can use ArgumentCaptor for this. Is that really the only way to do this? Is this possible at all with Hamcrest matchers?

Answer 1

The argThat return type is not being inferred for some reason. Try explicitly casting as shown below:

 Mockito.verify(foo).bar((Map<String, String>) argThat(Matchers.hasEntry("paramName", "paramValue")));

The testHasEntryCast() can be fixed as shown below. Notice that cast (Map<String, ?>) is to argThat return type:

@Test
public void testHasEntryCast() {
    Service mockService = mock(Service.class);
    Foo foo = new Foo(mockService);

    foo.bar();

    verify(mockService).activate((Map<String, ?>)  argThat(hasEntry("paramName", "paramValue")));
}