Java REST API unit testing is used with MockMVC to efficiently verify interface behavior. 1. Initialize MockMVC. The most commonly used @WebMvcTest annotation to automatically configure it, or manually build it through MockMvcBuilders; 2. When simulating a request, HTTP methods such as GET and POST can be implemented through chain calls and combined with assertion verification results; 3. To handle authentication, spring-security-test can be introduced and users can be simulated using @WithMockUser; 4. Pay attention to common pitfalls such as controller scanning, JSON format, CORS impact and assertion methods.
When writing Java's REST API, unit testing is an inescapable link. Using MockMVC to do unit testing is a convenient and practical choice. It can simulate HTTP requests and verify interface behavior without actually starting the server, which is efficient and low-cost.
Here are some questions and practices you may be concerned about:
How to initialize MockMVC
The most common way to use MockMVC in your test is to load Spring MVC configuration via the @WebMvcTest annotation. This annotation will automatically configure the MockMVC instance and only load the Controller-related beans, excluding the database-related parts.
@WebMvcTest(MyController.class)
class MyControllerTest {
@Autowired
private MockMvc mockMvc;
} If you are using a complete context (such as an integrated database), you can also use MockMvcBuilders.webAppContextSetup(context).build() to build it manually.
How to simulate various types of requests
GET, POST, PUT, DELETE can all be easily simulated. MockMVC provides a chained call method, with clear structure and easy assertion to return results.
For example, I want to test a GET interface /api/users/123 :
mockMvc.perform(get("/api/users/123"))
.andExpect(status().isOk())
.andExpect(jsonPath("$.name").value("John"));If it is POST, with JSON data, you can write it like this:
mockMvc.perform(post("/api/users")
.contentType(MediaType.APPLICATION_JSON)
.content("{\"name\":\"Alice\"}"))
.andExpect(status().isCreated());A few points to pay attention to:
- To set the correct
Content-Type - The JSON string format must be correct, or you can use
ObjectMapperto convert objects - If there are path parameters, you can directly splice them, such as
{id}/api/users/{id}id}
How to handle authentication and safety verification
Many REST APIs require permission control, such as the login status of JWT or Spring Security. At this time, the request will be intercepted.
One solution is to introduce spring-security-test , then inject UserDetailsService into the test class or create a test user.
The sample code is as follows:
@WithMockUser(username = "testuser", roles = {"USER"})
@Test
void shouldAccessSecuredApi() throws Exception {
mockMvc.perform(get("/api/private"))
.andExpect(status().isOk());
}This annotation can simulate the behavior of a logged-in user and avoid manually adding tokens every time.
Frequently Asked Questions and Precautions
Sometimes the test cannot run, it is not a logic problem, but a wrong configuration. Here are a few common pitfalls:
- The controller is not scanned : Make sure
@WebMvcTestspecifies the correct Controller class, or check the component scan range. - JSON parsing failed : There is a problem with the JSON format returned or sent. It is recommended to use
ObjectMapperto construct the data instead of hard-write strings. - Cross-domain issues do not affect MockMVC : Because it is a mock request, the CORS setting will not take effect, but the real environment may error.
- Don't rely on log output to determine right or wrong : use
.andExpect(...)to clearly assert the status code, content, etc.
Basically that's it. MockMVC is a very practical tool. Although it is a bit long-winded at the beginning, it can write quickly after getting familiar with it and cover most scenarios.
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