Automate REST API Testing Using Spring Test Framework

Advantages of Spring Boot test framework

• A request can be easily prepared and send over the internet
• Assertions in Response data
• Clean code which is easy to be maintained

The spring-boot-starter-test “Starter” (in the test scope) contains the following provided libraries:

• JUnit: The de-facto standard for unit testing Java applications.
• Spring Test & Spring Boot Test: Utilities and integration test support for Spring Boot applications.
• AssertJ: A fluent assertion library.
• Hamcrest: A library of matcher objects (also known as constraints or predicates).
• Mockito: A Java mocking framework.
• JSONassert: An assertion library for JSON.
• JsonPath: XPath for JSON.

These common libraries are very useful in writing tests. Spring boot also allows adding additional test dependencies of your own.

You can write code for unit testing and integration testing using Spring TestContext Framework. With this framework, it is possible to perform integration testing without requiring the deployment of your application or needing to connect to other infrastructure.

Testing with a running server

If you need to start a full running server then use random ports. If you use @SpringBootTest(webEnvironment=WebEnvironment.RANDOM_PORT), an available port is picked at random each time your test runs.

The @LocalServerPort annotation can be used to inject the actual port used into your test. For convenience, tests that need to make REST calls to the started server can additionally @Autowire a WebTestClient which resolves relative links to the running server and comes with a dedicated API for verifying responses, as shown in the following example:

Mocking Beans

When running tests, it is sometimes necessary to mock certain components within your application context. For example, you may have a facade over some remote service that is unavailable during development. Mocking can also be useful when you want to simulate failures that might be hard to trigger in a real environment.

Spring Boot includes a @MockBean annotation that can be used to define a Mockito mock for a bean inside your ApplicationContext. You can use the annotation to add new beans or replace a single existing bean definition. The annotation can be used directly on test classes, on fields within your test, or on @Configuration classes and fields. When used on a field, the instance of the created mock is also injected. Mock beans are automatically reset after each test method.

The following example replaces an existing RemoteService bean with a mock implementation: