How to use mockito for testing a REST service?

Question

I am very new in Java Unit Testing and I heard that Mockito framework is really good for testing purposes.

I have developed a REST Server (CRUD methods) and now I want to test it, but I don't know how?

Even more I don't know how this testing procedure should begin. My server should work on localhost and then make calls on that url(e.g. localhost:8888)?

Here is what I tried so far, but I'm pretty sure that this isn't the right way.

    @Test
    public void testInitialize() {
        RESTfulGeneric rest = mock(RESTfulGeneric.class);

        ResponseBuilder builder = Response.status(Response.Status.OK);

        builder = Response.status(Response.Status.OK).entity(
                "Your schema was succesfully created!");

        when(rest.initialize(DatabaseSchema)).thenReturn(builder.build());

        String result = rest.initialize(DatabaseSchema).getEntity().toString();

        System.out.println("Here: " + result);

        assertEquals("Your schema was succesfully created!", result);

    }

Here is the code for initialize method.

    @POST
    @Produces(MediaType.APPLICATION_JSON)
    @Path("/initialize")
    public Response initialize(String DatabaseSchema) {

        /** Set the LogLevel to Info, severe, warning and info will be written */
        LOGGER.setLevel(Level.INFO);

        ResponseBuilder builder = Response.status(Response.Status.OK);

        LOGGER.info("POST/initialize - Initialize the " + user.getUserEmail()
                + " namespace with a database schema.");

        /** Get a handle on the datastore itself */
        DatastoreService datastore = DatastoreServiceFactory
                .getDatastoreService();


        datastore.put(dbSchema);

        builder = Response.status(Response.Status.OK).entity(
                "Your schema was succesfully created!");
        /** Send response */
        return builder.build();
    }

In this test case I want to send a Json string to the server(POST). If everything went well then the server should reply with "Your schema was succesfully created!".

Can someone please help me?

Answer 1

OK. So, the contract of the method is the following: Parse the input string as JSON, and send back BAD_REQUEST if it's invalid. If it's valid, create an entity in the datastore with various properties (you know them), and send back OK.

And you need to verify that this contract is fulfilled by the method.

Where does Mockito help here? Well, if you test this method without Mockito, you need a real DataStoreService, and you need to verify that the entity has been created correctly in this real DataStoreService. This is where your test is not a unit test anymore, and this is also where it's too complex to test, too long, and too hard to run because it needs a complex environment.

Mockito can help by mocking the dependency on the DataStoreService: you can create a mock of DataStoreService, and verify that this mock is indeed called with the appropriate entity argument when you call your initialize() method in your test.

To do that, you need to be able to inject the DataStoreService into your object under test. It can be as easy as refactoring your object in the following way:

public class MyRestService {
    private DataStoreService dataStoreService;

    // constructor used on the server
    public MyRestService() {
        this.dataStoreService = DatastoreServiceFactory.getDatastoreService();
    }

    // constructor used by the unit tests
    public MyRestService(DataStoreService dataStoreService) {
        this.dataStoreService = dataStoreService;
    }

    public Response initialize(String DatabaseSchema) {
         ...
         // use this.dataStoreService instead of datastore
    }
}

And now in your test method, you can do:

@Test
public void testInitializeWithGoodInput() {
    DataStoreService mockDataStoreService = mock(DataStoreService.class);
    MyRestService service = new MyRestService(mockDataStoreService);
    String goodInput = "...";
    Response response = service.initialize(goodInput);
    assertEquals(Response.Status.OK, response.getStatus());

    ArgumentCaptor<Entity> argument = ArgumentCaptor.forClass(Entity.class);
    verify(mock).put(argument.capture());
    assertEquals("the correct kind", argument.getValue().getKind());
    // ... other assertions
}

Answer 2

What you're talking about sounds more like integration testing and Mockito (or any other mocking frameworks) will not be of much use to you.

If you want to unit test code you've written, Mockito is certainly a useful tool.

I suggest you read more about mocking/unit testing and which circumstances it should be used in.

Answer 3

Mockito is (generally) for testing portions of code; for example if you were consuming your REST service, but didn't want to do a full-stack test, you'd mock the service that connected to the REST service, allowing you to precisely, and consistently, test specific behavior.

To test internal portions of the REST service (e.g., a specific service method) without hitting a database, you'd mock the DB subsystem, allowing testing of service internals only, without involving the DB. This testing belongs in the REST service module, not the client side.

To test the REST service itself you'd use an actual client library, creating a full-stack integration test. Mockito could be used here to mock portions of the client unrelated to REST service consumption.

Answer 4

Best method is to use wiremock Add the following dependencies com.github.tomakehurst wiremock 2.4.1 org.igniterealtime.smack smack-core 4.0.6

Define and use the wiremock as shown below

@Rule
public WireMockRule wireMockRule = new WireMockRule(8089);

String response ="Hello world";
StubMapping responseValid = stubFor(get(urlEqualTo(url)).withHeader("Content-Type", equalTo("application/json"))
        .willReturn(aResponse().withStatus(200)
                .withHeader("Content-Type", "application/json").withBody(response)));

Answer 5

I agree this is not unit testing but integration test, anyway you'd rather take a look at the jersey and embedded grizzly server tests. To summ it up, this code starts the grizzly server (which could start the datbase as well) at localhost:8888, then setup client's jersey's client and sents a POST request which response should be tested. This is an integration since you're testing both server and database, you may use mockito to emulate the database however, but it depends how tied your server and database are.

(test using jersey 1.11 and grizzly 2.2)

    @BeforeClass
    public static void setUpClass() throws Exception {
        // starts grizzly
        Starter.start_grizzly(true);
        Thread.sleep(4000);
    }

    @Before
    public void setUp() throws Exception {
        client = new Client();
        webResource = client.resource("http://localhost:8888");
    }   

    @Test
    public void testPostSchemaDatabase() throws Exception {
        {
            String DatabaseSchema = "{ database_schema : {...}}";
            logger.info("REST client configured to send: "  + DatabaseSchema);
            ClientResponse response =  
                    webResource
                             .path("/initialize")
                             .type("application/json")
                             .post(ClientResponse.class, DatabaseSchema);
            //wait for the server to process
            Thread.sleep(2000);
            assertEquals(response.getStatus(), 204);    
            //test the response
        }       
    }

    @After
    public void after() throws JSONException
    {
            //probably you want to delete the schema at database and stop the server

}