Wiremock - Testcontainers Demo

This project aims to show how to use Testcontainers for Java to spin up a Docker container with a service providing a REST API for testing purposes. It also demonstrates using WireMock to proxy this service and inject delays or faults for specific endpoints.

We'll use this setup to test the integration between two very simple Spring Boot applications. Namely, a client app, and a server app which expose a REST API.

Let's look over the break down of IntegrationTest.java

JUnit5 Extensions

@Testcontainers
@WireMockTest(httpPort = IntegrationTest.WIREMOCK_PORT)
class IntegrationTest {
    // ...
}

The @Testcontainers and @WireMockTest class-level annotations are JUnit5 extensions. They will help us manage the lifecycle of the Testcontainer and the WireMock server.

Docker Compose Container

@Container
static DockerComposeContainer<?> env = new DockerComposeContainer<>(new File("src/test/resources/compose-test.yml"))
  .withExposedService("conversion-rates-api", 8080, Wait.forHttp("/currencies").forStatusCode(200)) 
  .withLocalCompose(true);

DockerComposeContainer<?> env Sets up a Docker Compose environment using the compose-test.yml file.

.withExposedService("conversion-rates-api", 8080, Wait.forHttp("/currencies").forStatusCode(200)) Exposes our REST API service on port 8080 and waits until the /currencies endpoint returns a 200 status code.

WireMock Stubs

String testcontainerUrl = "http://%s:%s".formatted(
  env.getServiceHost("conversion-rates-api", 8080),
  env.getServicePort("conversion-rates-api", 8080)
);

stubFor(get(urlMatching("/currencies/.*"))
  .willReturn(aResponse().proxiedFrom(testcontainerUrl)));

testcontainerUrl Constructs the URL for the conversion-rates-api service, running in the Docker container launched by Testcontainers.

stubFor(...).willReturn(aResponse().proxiedFrom(...) Sets up a stub for any GET request for the path /currencies and proxies the response from testcontainerUrl.

Injecting Failures and Delays

stubFor(get(urlMatching("/currencies/GBP"))
  .willReturn(aResponse()
    .withBody("Wrong response, definitely not a number!")));

stubFor(get(urlMatching("/currencies/RON"))
  .willReturn(aResponse()
    .withFixedDelay(3_000)
      .proxiedFrom(testcontainerUrl)));

Testing

var okResponse = exchange.toEuro(100.00, "USD");
assertThat(okResponse)
  .extracting(ResponseEntity::getStatusCode, ResponseEntity::getBody)
  .containsExactly(HttpStatus.OK, "Exchanging 100.0 USD at a rate of 0.92 will give you 92.0 EUR");

// and
var nokResponse = exchange.toEuro(100.00, "GBP");
assertThat(nokResponse)
  .extracting(ResponseEntity::getStatusCode, ResponseEntity::getBody)
  .containsExactly(HttpStatus.INTERNAL_SERVER_ERROR, "Ooops! There was an error on our side!");

// and
var slowResponse = exchange.toEuro(100.00, "RON");
assertThat(slowResponse.getStatusCode())
  .isEqualTo(HttpStatus.GATEWAY_TIMEOUT);