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Testing REST API integrations using WireMock

Learn how to create a Spring Boot application that integrates with external REST APIs, then test those integrations using Testcontainers and WireMock.

Table of contents

In this guide, you'll learn how to:

  • Create a Spring Boot application that talks to external REST APIs
  • Test external API integrations using WireMock with both the JUnit 5 extension and the Testcontainers WireMock module

Prerequisites

  • Java 17+
  • Maven or Gradle
  • A Docker environment supported by Testcontainers
Note

If you're new to Testcontainers, visit the Testcontainers overview to learn more about Testcontainers and the benefits of using it.

Create the Spring Boot project

Set up the project

Create a Spring Boot project from Spring Initializr by selecting the Spring Web and Testcontainers starters.

Alternatively, clone the guide repository.

After generating the project, add the REST Assured, WireMock, and WireMock Testcontainers module libraries as test dependencies. The key dependencies in pom.xml are:

<properties>
    <java.version>17</java.version>
    <testcontainers.version>2.0.4</testcontainers.version>
    <wiremock-testcontainers.version>1.0-alpha-13</wiremock-testcontainers.version>
</properties>
<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.testcontainers</groupId>
        <artifactId>testcontainers-junit-jupiter</artifactId>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.wiremock</groupId>
        <artifactId>wiremock-standalone</artifactId>
        <version>3.6.0</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.wiremock.integrations.testcontainers</groupId>
        <artifactId>wiremock-testcontainers-module</artifactId>
        <version>${wiremock-testcontainers.version}</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>io.rest-assured</groupId>
        <artifactId>rest-assured</artifactId>
        <scope>test</scope>
    </dependency>
</dependencies>

Using the Testcontainers BOM (Bill of Materials) is recommended so that you don't have to repeat the version for every Testcontainers module dependency.

This guide builds an application that manages video albums. A third-party REST API handles photo assets. For demonstration purposes, the application uses the publicly available JSONPlaceholder API as a photo service.

The application exposes a GET /api/albums/{albumId} endpoint that calls the photo service to fetch photos for a given album. WireMock is a tool for building mock APIs. Testcontainers provides a WireMock module that runs WireMock as a Docker container.

Create the Album and Photo models

Create Album.java using Java records:

package com.testcontainers.demo;

import java.util.List;

public record Album(Long albumId, List<Photo> photos) {}

record Photo(Long id, String title, String url, String thumbnailUrl) {}

Create the PhotoServiceClient

Create PhotoServiceClient.java, which uses RestTemplate to fetch photos for a given album ID:

package com.testcontainers.demo;

import java.util.List;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.core.ParameterizedTypeReference;
import org.springframework.http.HttpMethod;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

@Service
class PhotoServiceClient {

  private final String baseUrl;
  private final RestTemplate restTemplate;

  PhotoServiceClient(
    @Value("${photos.api.base-url}") String baseUrl,
    RestTemplateBuilder builder
  ) {
    this.baseUrl = baseUrl;
    this.restTemplate = builder.build();
  }

  List<Photo> getPhotos(Long albumId) {
    String url = baseUrl + "/albums/{albumId}/photos";
    ResponseEntity<List<Photo>> response = restTemplate.exchange(
      url,
      HttpMethod.GET,
      null,
      new ParameterizedTypeReference<>() {},
      albumId
    );
    return response.getBody();
  }
}

The photo service base URL is externalized as a configuration property. Add the following entry to src/main/resources/application.properties:

photos.api.base-url=https://jsonplaceholder.typicode.com

Create the REST API endpoint

Create AlbumController.java:

package com.testcontainers.demo;

import java.util.List;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestClientResponseException;

@RestController
@RequestMapping("/api")
class AlbumController {

  private static final Logger logger = LoggerFactory.getLogger(
    AlbumController.class
  );

  private final PhotoServiceClient photoServiceClient;

  AlbumController(PhotoServiceClient photoServiceClient) {
    this.photoServiceClient = photoServiceClient;
  }

  @GetMapping("/albums/{albumId}")
  public ResponseEntity<Album> getAlbumById(@PathVariable Long albumId) {
    try {
      List<Photo> photos = photoServiceClient.getPhotos(albumId);
      return ResponseEntity.ok(new Album(albumId, photos));
    } catch (RestClientResponseException e) {
      logger.error("Failed to get photos", e);
      return new ResponseEntity<>(e.getStatusCode());
    }
  }
}

This endpoint calls the photo service for a given album ID and returns a response like:

{
  "albumId": 1,
  "photos": [
    {
      "id": 51,
      "title": "non sunt voluptatem placeat consequuntur rem incidunt",
      "url": "https://via.placeholder.com/600/8e973b",
      "thumbnailUrl": "https://via.placeholder.com/150/8e973b"
    },
    {
      "id": 52,
      "title": "eveniet pariatur quia nobis reiciendis laboriosam ea",
      "url": "https://via.placeholder.com/600/121fa4",
      "thumbnailUrl": "https://via.placeholder.com/150/121fa4"
    }
  ]
}

Write tests with WireMock and Testcontainers

Mocking external API interactions at the HTTP protocol level, rather than mocking Java methods, lets you verify marshalling and unmarshalling behavior and simulate network issues.

Test using WireMock JUnit 5 extension

WireMock provides a JUnit 5 extension that starts an in-process WireMock server. You can configure stub responses using the WireMock Java API.

Create AlbumControllerTest.java:

package com.testcontainers.demo;

import static com.github.tomakehurst.wiremock.client.WireMock.aResponse;
import static com.github.tomakehurst.wiremock.client.WireMock.urlMatching;
import static com.github.tomakehurst.wiremock.core.WireMockConfiguration.wireMockConfig;
import static io.restassured.RestAssured.given;
import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.Matchers.hasSize;
import static org.springframework.boot.test.context.SpringBootTest.WebEnvironment.RANDOM_PORT;

import com.github.tomakehurst.wiremock.client.WireMock;
import com.github.tomakehurst.wiremock.junit5.WireMockExtension;
import io.restassured.RestAssured;
import io.restassured.http.ContentType;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.RegisterExtension;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.web.server.LocalServerPort;
import org.springframework.http.MediaType;
import org.springframework.test.context.DynamicPropertyRegistry;
import org.springframework.test.context.DynamicPropertySource;

@SpringBootTest(webEnvironment = RANDOM_PORT)
class AlbumControllerTest {

  @LocalServerPort
  private Integer port;

  @RegisterExtension
  static WireMockExtension wireMock = WireMockExtension
    .newInstance()
    .options(wireMockConfig().dynamicPort())
    .build();

  @DynamicPropertySource
  static void configureProperties(DynamicPropertyRegistry registry) {
    registry.add("photos.api.base-url", wireMock::baseUrl);
  }

  @BeforeEach
  void setUp() {
    RestAssured.port = port;
  }

  @Test
  void shouldGetAlbumById() {
    Long albumId = 1L;

    wireMock.stubFor(
      WireMock
        .get(urlMatching("/albums/" + albumId + "/photos"))
        .willReturn(
          aResponse()
            .withHeader("Content-Type", MediaType.APPLICATION_JSON_VALUE)
            .withBody(
              """
              [
                   {
                       "id": 1,
                       "title": "accusamus beatae ad facilis cum similique qui sunt",
                       "url": "https://via.placeholder.com/600/92c952",
                       "thumbnailUrl": "https://via.placeholder.com/150/92c952"
                   },
                   {
                       "id": 2,
                       "title": "reprehenderit est deserunt velit ipsam",
                       "url": "https://via.placeholder.com/600/771796",
                       "thumbnailUrl": "https://via.placeholder.com/150/771796"
                   }
               ]
              """
            )
        )
    );

    given()
      .contentType(ContentType.JSON)
      .when()
      .get("/api/albums/{albumId}", albumId)
      .then()
      .statusCode(200)
      .body("albumId", is(albumId.intValue()))
      .body("photos", hasSize(2));
  }

  @Test
  void shouldReturnServerErrorWhenPhotoServiceCallFailed() {
    Long albumId = 2L;
    wireMock.stubFor(
      WireMock
        .get(urlMatching("/albums/" + albumId + "/photos"))
        .willReturn(aResponse().withStatus(500))
    );

    given()
      .contentType(ContentType.JSON)
      .when()
      .get("/api/albums/{albumId}", albumId)
      .then()
      .statusCode(500);
  }
}

Here's what the test does:

  • @SpringBootTest starts the full application on a random port.
  • @RegisterExtension creates a WireMockExtension that starts WireMock on a dynamic port.
  • @DynamicPropertySource overrides photos.api.base-url to point at the WireMock endpoint, so the application talks to WireMock instead of the real photo service.
  • shouldGetAlbumById() configures a stub response for /albums/{albumId}/photos, sends a request to the application's /api/albums/{albumId} endpoint, and verifies the response body.
  • shouldReturnServerErrorWhenPhotoServiceCallFailed() configures WireMock to return a 500 status and verifies that the application propagates that status to the caller.

Stub using JSON mapping files

Instead of using the WireMock Java API, you can configure stubs with JSON mapping files. Create src/test/resources/wiremock/mappings/get-album-photos.json:

{
  "mappings": [
    {
      "request": {
        "method": "GET",
        "urlPattern": "/albums/([0-9]+)/photos"
      },
      "response": {
        "status": 200,
        "headers": {
          "Content-Type": "application/json"
        },
        "bodyFileName": "album-photos-resp-200.json"
      }
    },
    {
      "request": {
        "method": "GET",
        "urlPattern": "/albums/2/photos"
      },
      "response": {
        "status": 500,
        "headers": {
          "Content-Type": "application/json"
        }
      }
    },
    {
      "request": {
        "method": "GET",
        "urlPattern": "/albums/3/photos"
      },
      "response": {
        "status": 200,
        "headers": {
          "Content-Type": "application/json"
        },
        "jsonBody": []
      }
    }
  ]
}

Create the response body file at src/test/resources/wiremock/__files/album-photos-resp-200.json:

[
  {
    "id": 1,
    "title": "accusamus beatae ad facilis cum similique qui sunt",
    "url": "https://via.placeholder.com/600/92c952",
    "thumbnailUrl": "https://via.placeholder.com/150/92c952"
  },
  {
    "id": 2,
    "title": "reprehenderit est deserunt velit ipsam",
    "url": "https://via.placeholder.com/600/771796",
    "thumbnailUrl": "https://via.placeholder.com/150/771796"
  }
]

Initialize WireMock to load stubs from the mapping files:

@RegisterExtension
static WireMockExtension wireMockServer = WireMockExtension
  .newInstance()
  .options(
    wireMockConfig().dynamicPort().usingFilesUnderClasspath("wiremock")
  )
  .build();

With mapping-based stubs in place, create AlbumControllerWireMockMappingTests.java:

package com.testcontainers.demo;

import static com.github.tomakehurst.wiremock.core.WireMockConfiguration.wireMockConfig;
import static io.restassured.RestAssured.given;
import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.Matchers.hasSize;
import static org.springframework.boot.test.context.SpringBootTest.WebEnvironment.RANDOM_PORT;

import com.github.tomakehurst.wiremock.junit5.WireMockExtension;
import io.restassured.RestAssured;
import io.restassured.http.ContentType;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.RegisterExtension;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.web.server.LocalServerPort;
import org.springframework.test.context.DynamicPropertyRegistry;
import org.springframework.test.context.DynamicPropertySource;

@SpringBootTest(webEnvironment = RANDOM_PORT)
class AlbumControllerWireMockMappingTests {

  @LocalServerPort
  private Integer port;

  @RegisterExtension
  static WireMockExtension wireMockServer = WireMockExtension
    .newInstance()
    .options(
      wireMockConfig().dynamicPort().usingFilesUnderClasspath("wiremock")
    )
    .build();

  @DynamicPropertySource
  static void configureProperties(DynamicPropertyRegistry registry) {
    registry.add("photos.api.base-url", wireMockServer::baseUrl);
  }

  @BeforeEach
  void setUp() {
    RestAssured.port = port;
  }

  @Test
  void shouldGetAlbumById() {
    Long albumId = 1L;

    given()
      .contentType(ContentType.JSON)
      .when()
      .get("/api/albums/{albumId}", albumId)
      .then()
      .statusCode(200)
      .body("albumId", is(albumId.intValue()))
      .body("photos", hasSize(2));
  }

  @Test
  void shouldReturnServerErrorWhenPhotoServiceCallFailed() {
    Long albumId = 2L;

    given()
      .contentType(ContentType.JSON)
      .when()
      .get("/api/albums/{albumId}", albumId)
      .then()
      .statusCode(500);
  }

  @Test
  void shouldReturnEmptyPhotos() {
    Long albumId = 3L;

    given()
      .contentType(ContentType.JSON)
      .when()
      .get("/api/albums/{albumId}", albumId)
      .then()
      .statusCode(200)
      .body("albumId", is(albumId.intValue()))
      .body("photos", hasSize(0));
  }
}

The tests don't need inline stub definitions because WireMock loads the mappings automatically from the classpath.

Test using the Testcontainers WireMock module

The Testcontainers WireMock module provisions WireMock as a standalone Docker container, based on WireMock Docker. This approach is useful when you want complete isolation between the test JVM and the mock server.

Create a mock configuration file at src/test/resources/com/testcontainers/demo/AlbumControllerTestcontainersTests/mocks-config.json:

{
  "mappings": [
    {
      "request": {
        "method": "GET",
        "urlPattern": "/albums/([0-9]+)/photos"
      },
      "response": {
        "status": 200,
        "headers": {
          "Content-Type": "application/json"
        },
        "bodyFileName": "album-photos-response.json"
      }
    },
    {
      "request": {
        "method": "GET",
        "urlPattern": "/albums/2/photos"
      },
      "response": {
        "status": 500,
        "headers": {
          "Content-Type": "application/json"
        }
      }
    },
    {
      "request": {
        "method": "GET",
        "urlPattern": "/albums/3/photos"
      },
      "response": {
        "status": 200,
        "headers": {
          "Content-Type": "application/json"
        },
        "jsonBody": []
      }
    }
  ]
}

Create the response body file at src/test/resources/com/testcontainers/demo/AlbumControllerTestcontainersTests/album-photos-response.json:

[
  {
    "id": 1,
    "title": "accusamus beatae ad facilis cum similique qui sunt",
    "url": "https://via.placeholder.com/600/92c952",
    "thumbnailUrl": "https://via.placeholder.com/150/92c952"
  },
  {
    "id": 2,
    "title": "reprehenderit est deserunt velit ipsam",
    "url": "https://via.placeholder.com/600/771796",
    "thumbnailUrl": "https://via.placeholder.com/150/771796"
  }
]

Create AlbumControllerTestcontainersTests.java:

package com.testcontainers.demo;

import static io.restassured.RestAssured.given;
import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.Matchers.hasSize;
import static org.springframework.boot.test.context.SpringBootTest.WebEnvironment.RANDOM_PORT;

import io.restassured.RestAssured;
import io.restassured.http.ContentType;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.web.server.LocalServerPort;
import org.springframework.test.context.DynamicPropertyRegistry;
import org.springframework.test.context.DynamicPropertySource;
import org.testcontainers.junit.jupiter.Container;
import org.testcontainers.junit.jupiter.Testcontainers;
import org.wiremock.integrations.testcontainers.WireMockContainer;

@SpringBootTest(webEnvironment = RANDOM_PORT)
@Testcontainers
class AlbumControllerTestcontainersTests {

  @LocalServerPort
  private Integer port;

  @Container
  static WireMockContainer wiremockServer = new WireMockContainer(
    "wiremock/wiremock:3.6.0"
  )
    .withMapping(
      "photos-by-album",
      AlbumControllerTestcontainersTests.class,
      "mocks-config.json"
    )
    .withFileFromResource(
      "album-photos-response.json",
      AlbumControllerTestcontainersTests.class,
      "album-photos-response.json"
    );

  @DynamicPropertySource
  static void configureProperties(DynamicPropertyRegistry registry) {
    registry.add("photos.api.base-url", wiremockServer::getBaseUrl);
  }

  @BeforeEach
  void setUp() {
    RestAssured.port = port;
  }

  @Test
  void shouldGetAlbumById() {
    Long albumId = 1L;

    given()
      .contentType(ContentType.JSON)
      .when()
      .get("/api/albums/{albumId}", albumId)
      .then()
      .statusCode(200)
      .body("albumId", is(albumId.intValue()))
      .body("photos", hasSize(2));
  }

  @Test
  void shouldReturnServerErrorWhenPhotoServiceCallFailed() {
    Long albumId = 2L;

    given()
      .contentType(ContentType.JSON)
      .when()
      .get("/api/albums/{albumId}", albumId)
      .then()
      .statusCode(500);
  }

  @Test
  void shouldReturnEmptyPhotos() {
    Long albumId = 3L;

    given()
      .contentType(ContentType.JSON)
      .when()
      .get("/api/albums/{albumId}", albumId)
      .then()
      .statusCode(200)
      .body("albumId", is(albumId.intValue()))
      .body("photos", hasSize(0));
  }
}

Here's what the test does:

  • The @Testcontainers and @Container annotations start a WireMockContainer using the wiremock/wiremock:3.6.0 Docker image.
  • withMapping() loads stub mappings from mocks-config.json, and withFileFromResource() loads the response body file.
  • @DynamicPropertySource overrides photos.api.base-url to point at the WireMock container's base URL.
  • The tests don't contain inline stub definitions because WireMock loads them from the JSON configuration files.

Run tests and next steps

Run the tests

$ ./mvnw test

Or with Gradle:

$ ./gradlew test

You should see the WireMock Docker container start in the console output. It acts as the photo service, serving mock responses based on the configured expectations. All tests should pass.

Summary

You built a Spring Boot application that integrates with an external REST API, then tested that integration using three different approaches:

  • WireMock JUnit 5 extension with inline stubs
  • WireMock JUnit 5 extension with JSON mapping files
  • Testcontainers WireMock module running WireMock in a Docker container

Testing at the HTTP protocol level instead of mocking Java methods lets you catch serialization issues and simulate realistic failure scenarios.

To learn more about Testcontainers, visit the Testcontainers overview.

Further reading