@MockBean doesn't work for @WebMvcTest with JUnit 5 and Sping Boot 2?

Question

I researched similar questions on StackOverflow and cannot find a root cause in my case.

CONTEXT:

I have @RestController in SpringBoot 2 with dependency on BookSearcherService. I want to mock BookSearcherService in order to unit-test controller.

ERROR:

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.NullPointerException at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1013) at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:897) at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882) at org.springframework.test.web.servlet.TestDispatcherServlet.service(TestDispatcherServlet.java:71) at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) at org.springframework.mock.web.MockFilterChain$ServletFilterProxy.doFilter(MockFilterChain.java:166) at org.springframework.mock.web.MockFilterChain.doFilter(MockFilterChain.java:133) at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.springframework.mock.web.MockFilterChain.doFilter(MockFilterChain.java:133) at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.springframework.mock.web.MockFilterChain.doFilter(MockFilterChain.java:133) at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.springframework.mock.web.MockFilterChain.doFilter(MockFilterChain.java:133) at org.springframework.test.web.servlet.MockMvc.perform(MockMvc.java:182) at com.search.book.Booksearcher.controller.BookSearcherControllerMockMvcTest.canListAll(BookSearcherControllerMockMvcTest.java:54) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:532) at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:115) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:171) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:72) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:167) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:114) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:59) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$4(NodeTestTask.java:108) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:72) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:98) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:74) at java.util.ArrayList.forEach(ArrayList.java:1257) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$4(NodeTestTask.java:112) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:72) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:98) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:74) at java.util.ArrayList.forEach(ArrayList.java:1257) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$4(NodeTestTask.java:112) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:72) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:98) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:74) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32) at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57) at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:220) at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$6(DefaultLauncher.java:188) at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:202) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:181) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:128) at org.eclipse.jdt.internal.junit5.runner.JUnit5TestReference.run(JUnit5TestReference.java:89) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:541) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:763) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:463) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:209) Caused by: java.lang.NullPointerException at com.search.book.Booksearcher.controller.BookSearcherController.listAll(BookSearcherController.java:31) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:189) at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:892) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:797) at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1038) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) ... 59 more

CODE:

BookSearcherController.java:

@RestController
@RequestMapping("/book")
@RequiredArgsConstructor
public class BookSearcherController {

    private BookSearcherService bookSearcherService;

    @GetMapping(path = "/list", produces = { "application/json" })
    @ResponseBody
    public List<BookDto> listAll() {
        return bookSearcherService.listAll();
    }
}

BookSearcherService.java:

@Service
public class BookSearcherService {

    private BookSearcherCrudService bookSearcherCrudService;

    @Autowired
    void setBookSearcherRepository(BookSearcherCrudService bookSearcherCrudService) {
        this.bookSearcherCrudService = bookSearcherCrudService;
    }

    private BookSearcherRepository bookSearcherRepository;

    @Autowired
    void setBookSearcherRepository(BookSearcherRepository bookSearcherRepository) {
        this.bookSearcherRepository = bookSearcherRepository;
    }

    public List<BookDto> listAll() {
        List<Book> books = bookSearcherRepository.findAll();
        return books.stream()
                .map(bookSearcherCrudService::toDto)
                .collect(Collectors.toList());
    }
}

BookSearcherControllerMockMvcTest.java:

@WebMvcTest(controllers = BookSearcherController.class)
public class BookSearcherControllerMockMvcTest {

    @Autowired
    private MockMvc mockMvc;

    @MockBean
    private BookSearcherService bookSearcherService;

    @Autowired
    private ObjectMapper objectMapper;

    @Test
    public void canListAll() throws Exception {
        assertThat(bookSearcherService).isNotNull();
        assertThat(mockMvc).isNotNull();

        List<BookDto> books = asList(new BookDto("Title 1"), new BookDto("Title 2"), new BookDto("Title 3"));

        given(bookSearcherService.listAll()).willReturn(books);

        ResultActions perform = mockMvc.perform(get("/book/list"));
    }
}

POM.XML

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.4.RELEASE</version>
        <relativePath /> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.search.book</groupId>
    <artifactId>book-searcher</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>book-searcher</name>
    <description>Project for books search</description>

    <properties>
        <java.version>1.8</java.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-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.flywaydb</groupId>
            <artifactId>flyway-core</artifactId>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>junit</groupId>
                    <artifactId>junit</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-all</artifactId>
            <version>1.9.5</version>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-engine</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.platform</groupId>
            <artifactId>junit-platform-launcher</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.platform</groupId>
            <artifactId>junit-platform-runner</artifactId>
            <scope>test</scope>
        </dependency>


    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

QUESTION:

The issue as I stated above is that BookSearcherService when perform call on mockMvc has null. It means that either @MockBean doesn't work or I did an error which cannot spot for several hours. I am using Java8.

Answer 1

The problem is that bookSearcherService doesn’t get injected in BookSearchController because it’s using @RequiredArgsConstructor which in this case does not create a correct constructor.

The @RequiredArgsConstructor documentation states that a constructor will be created with parameters for uninitialized final or @NonNull fields. However, bookSearcherService is neither and therefore it's not added as a constructor parameter.

So while the mock itself is not null, it’s never injected to the tested controller.