java.lang.LinkageError: loader constraint violation When trying to use Mockito Argument Matcher

Question

I am trying to test a class and I have my own argument Mathcher to match the arguments. Here is the code:

 @Test
public void testDoBindModelsToForm()
{
    OrganizationToRelatedSubregionsConverter organizationToRelatedSubregionsConverter = mock(OrganizationToRelatedSubregionsConverter.class);
    List<Organization> subregion1 = new ArrayList<Organization>();

    Organization subregionOrg1 = CommonentityFactory.eINSTANCE.createOrganization();
    subregionOrg1.setMID(OrganizationMID.create(DOMAIN, 100L));
    subregionOrg1.setNameFormatted("Subregion 1"); //$NON-NLS-1$
    subregion1.add(subregionOrg1);
    when(
            organizationToRelatedSubregionsConverter.convert(Matchers
                    .argThat(new OrganizationMIDMatcher(catchmentArea1.getMID())))).thenReturn(
            subregion1);

    CatchmentFormController catchmentFormController = new CatchmentFormController(
            catchmentForm, DOMAIN, conversationDescriptor, configuration, registrationManager,
            catchment, null, LaunchMode.ADD, organizationToRelatedSubregionsConverter);

    catchmentFormController.renderDynamicForm();
    organizationToRelatedSubregionsConverter.convert(catchmentArea1.getMID());
}

And here is my custom Matcher class:

static class OrganizationMIDMatcher extends ArgumentMatcher<OrganizationMID>
{
    private OrganizationMID expectedOrganizationMID;

    public OrganizationMIDMatcher(OrganizationMID expectedOrganizationMID)
    {
        this.expectedOrganizationMID = expectedOrganizationMID;
    }

    @Override
    public boolean matches(Object argument)
    {
        if (argument != null && argument instanceof OrganizationMID)
        {
            OrganizationMID actualOrganization = (OrganizationMID) argument;
            return actualOrganization.equals(expectedOrganizationMID);
        }
        return false;
    }
}

When I run the test, I get the following error. The Mockito dependency I am using is Mockito-all 1.8.5.

  > java.lang.LinkageError: loader constraint violation:
 when resolving method "org.mockito.Matchers.argThat(Lorg/hamcrest/Matcher;)Ljava/lang/Object;" 
 the class loader (instance of org/eclipse/osgi/internal/baseadaptor/DefaultClassLoader)
 of the current class, com/cerner/registration/ui/internal/converters/OrganizationToRelatedSubregionsConverterTest,
 and the class loader
    (instance of org/eclipse/osgi/internal/baseadaptor/DefaultClassLoader) for resolved class,
 org/mockito/Matchers, have different Class objects for the type org/hamcrest/Matcher used in the signature

Any idea on what could be the problem here?

Answer 1

You should not use mockito-all with junit 4.8.2-v370. Both contain the hamcrest dependency, and as they use different classloaders in an OSGi environment, those classes will be incompatible. As a workaround, you should consider using mockito-core (1.8.5 if want to use the same version) and at least 4.9 version of junit (where they started to bundle hamcrest properly: as a dependency).

Alternatively -not to be followed- you can "fork" the 4.8.2 version of junit and repackage it without the hamcrest classes.