Contract Test Example

gistfile1.java

@RunWith(Parameterized.class)
public class ApiContractTest {
    private UrlValidator urlValidator = new UrlValidator(new String[]{"http","https"});
    private Api toTest;

    public ApiContractTest(Api impl, String name){
        this.toTest = impl;
    }

    @Parameterized.Parameters(name = "{1}")
    public static Collection<Object[]> generateData() throws IllegalAccessException, InstantiationException {
        Reflections reflections = new Reflections("org.scribe.builder.api");
        Set<Class<? extends Api>> allSubTypes = reflections.getSubTypesOf(Api.class);

        List<Object[]> allConcreteSubTypes = new ArrayList<>();
        for (Class<? extends Api> candidate : allSubTypes) {
            if(!Modifier.isAbstract(candidate.getModifiers())){
                allConcreteSubTypes.add(new Object[]{candidate.newInstance(), candidate.getSimpleName()});
            }
        }

        return allConcreteSubTypes;
    }

    @Test
    public void ifHasGrantTypeReturnsValidGrantType(){
        if(toTest.hasGrantType()){
            assertTrue("getGrantType Breaches the provider Api contract, " +
                    "If you specify the api uses grant_type you must provide a valid grant type", StringUtils.isNotBlank(toTest.getGrantType()));
        }
    }
}

The Parameters(name = "{1}") and the String name on the constructor are just another artifact of the clunkiness of junit paramterized tests. All this is doing is giving the tests a name instead of numbers.