Bean serialization issue while running test case

Question

when hit the endpoint from the browser it is working fine but test case failing. please find the code below:

Controller class:

@RestController
public class EmployeeController {

    @Autowired
    private EmployeeDTO employeeDTO;

  
    @GetMapping("/getEmployee")
    public EmployeeDTO getEmployee(){
        employeeDTO.setEmpId(1);
        employeeDTO.setEmpName("Bob");
        return employeeDTO;
    }

EmployeeDTOClass:

@Getter
@Setter
@NoArgsConstructor
@Component
public class EmployeeDTO {

    private int empId;
    private String empName;

}

EmployeeControllerTest class:

@WebMvcTest
public class EmployeeControllerTest {
    @Autowired
    private MockMvc mockmvc;

    @MockBean
    private EmployeeDTO employeeDTO;

    @Test
    public void testGetEmployee() throws Exception {
        RequestBuilder request = MockMvcRequestBuilders.get("/getEmployee");
        mockmvc.perform(request)
                .andExpect(status().isOk());
    }
}

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 https://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>2.7.8</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.spring</groupId>
    <artifactId>tennis</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>tennis</name>
    <description>Demo project</description>
    <properties>
        <java.version>11</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-test</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>5.7.0</version>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-engine</artifactId>
            <version>5.7.0</version>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.26</version>
            <scope>provided</scope>
        </dependency>

    </dependencies>

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

</project>

Exception when testcase is run:

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.http.converter.HttpMessageConversionException: Type definition error: [simple type, class org.mockito.internal.creation.bytebuddy.ByteBuddyCrossClassLoaderSerializationSupport]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class org.mockito.internal.creation.bytebuddy.ByteBuddyCrossClassLoaderSerializationSupport and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: com.spring.tennis.model.EmployeeDTO$MockitoMock$MCOb7jmM["mockitoInterceptor"]->org.mockito.internal.creation.bytebuddy.MockMethodInterceptor["serializationSupport"])

test case failing not sure why.

Answer 1

In your example, EmployeeDTO is a component. Usually it is not customary to return a bean as a response object for method. Although spring built-in object mapper handled your object and serialized it in json, apparently mockito built-in serializer/deserializer could not managed with it.

So, if you remove @Component annotation from EmployeeDTO then everything will work fine.

In a contoller, do something like:

@GetMapping("/getEmployee")
public EmployeeDTO getEmployee(){
    var employeeDTO = new EmployeeDTO();
    employeeDTO.setEmpId(1);
    employeeDTO.setEmpName("Bob");
    return employeeDTO;
}

And do not forget to remove @Autowired part.

Hope it will helps you.