15. Integration Testing

Integration and Functional Testing

Automated Testing Scope

• Unit Tests: Easiest to write and maintain, narrowest scope. Write the most of these.
• Integration Tests: Test the interaction between Units. Span multiple components.
• Functional Tests: Verify the behavior of your application from start to finish, including interaction with the UI and database.

Integration Testing

Common Integration Test Targets

• Database
• External APIs

Testing Databases

Use In-Memory Databases

• H2 database
• Hibernate can automatically construct database from your class definitions.
• Otherwise, you can use a SQL script that constructs the test database.

Interacting with Test Databases

• Basic Solution: Connect in @BeforeAll
• Spring Framework: Separate config file for tests
• Test Frameworks to Populate Test Databases: Unitils

Database Interaction and unit tests covered in greater detail in the Java Web Developer Nanodegree

Testing External APIs

WireMock

WireMock is a tool that allows you to programmatically create fake HTTP endpoints for external API integration testing.

This is an example class that connects to an external API to retrieve the value of fizzBuzz:

public class ExternalSalesService implements SalesService {

    private String resource;

    public ExternalSalesService(String resource) {
        this.resource = resource;
    }

    @Override
    public String fizzBuzz(int i) {
        //send a request to url/fizzbuzz/{i}
        HttpRequest request = HttpRequest.newBuilder(URI.create(resource + i)).GET().build();
        try {
            HttpResponse<String> response = HttpClient.newHttpClient()
                    .send(request, HttpResponse.BodyHandlers.ofString());
            return response.body();
        } catch (InterruptedException | IOException e) {
            throw new RuntimeException("Error retrieving value for " + i, e);
        }
    }
}

Writing an integration test that uses this class requires a valid http endpoint for it to use. Wiremock allows us to create that endpoint.

class ExternalSalesServiceTest {

    static WireMockServer wireMock = new WireMockServer(wireMockConfig().port(8089));
    private static String serverPath = "http://localhost:8089";
    private static String fizzBuzzPath = "/fizzbuzz/";

    ExternalSalesService fizzBuzzService;

    @BeforeAll
    static void setup() {
        wireMock.start();
    }
    @AfterAll
    static void cleanup() {
        wireMock.stop();
    }

    @BeforeEach
    void init() {
        wireMock.resetAll();
        fizzBuzzService = new ExternalSalesService(serverPath + fizzBuzzPath);
    }

    @Test
    public void externalFizzBuzz_passedValue_returnsExternalResponse() {
        int i = 3;
        String expected = "Fizz";
        wireMock.stubFor(get(urlEqualTo(fizzBuzzPath + i))
                .willReturn(aResponse().withStatus(200).withBody(expected)));
        String response = fizzBuzzService.fizzBuzz(i);
        assertEquals(expected, response);
    }

}