BAEL-6097: Pitfalls on Testing with Spring Boot (#13441)

* BAEL-6097: Create project

* BAEL-6097: Implement sample code and tests with custom test slices

* BAEL-6097: Fix application-test.yml

* BAEL-6097: Rename tests to match BDD naming strategy, add test for Mapper Integration Test

pom.xml

@@ -965,6 +965,7 @@
                 <module>spring-boot-modules/spring-boot-3</module>
                 <module>spring-boot-modules/spring-boot-3-native</module>
                 <module>spring-boot-modules/spring-boot-3-observation</module>
+                <module>spring-boot-modules/spring-boot-3-test-pitfalls</module>
                 <module>spring-swagger-codegen/custom-validations-opeanpi-codegen</module>
                 <module>testing-modules/testing-assertions</module>
                 <module>persistence-modules/fauna</module>
@@ -1163,6 +1164,7 @@
                 <module>spring-boot-modules/spring-boot-3</module>
                 <module>spring-boot-modules/spring-boot-3-native</module>
                 <module>spring-boot-modules/spring-boot-3-observation</module>
+                <module>spring-boot-modules/spring-boot-3-test-pitfalls</module>
                 <module>spring-swagger-codegen/custom-validations-opeanpi-codegen</module>
                 <module>testing-modules/testing-assertions</module>
                 <module>persistence-modules/fauna</module>
@@ -1283,7 +1285,7 @@
                 <java.version>11</java.version>
             </properties>
         </profile>
-        
+
         <profile>
             <id>parents</id>
             <modules>

spring-boot-modules/spring-boot-3-test-pitfalls/pom.xml

@@ -0,0 +1,87 @@
+<?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>
+    <artifactId>spring-boot-3-test-pitfalls</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>spring-boot-3-test-pitfalls</name>
+    <description>Demo project for Spring Boot Testing Pitfalls</description>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-boot-3</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../parent-boot-3</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-validation</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-devtools</artifactId>
+            <scope>runtime</scope>
+            <optional>true</optional>
+        </dependency>
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <optional>true</optional>
+        </dependency>
+        <dependency>
+            <groupId>org.mapstruct</groupId>
+            <artifactId>mapstruct</artifactId>
+            <version>${org.mapstruct.version}</version>
+            <optional>true</optional>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <pluginManagement>
+            <plugins>
+                <plugin>
+                    <groupId>org.apache.maven.plugins</groupId>
+                    <artifactId>maven-compiler-plugin</artifactId>
+                    <configuration>
+                        <annotationProcessorPaths>
+                            <path>
+                                <groupId>org.projectlombok</groupId>
+                                <artifactId>lombok</artifactId>
+                                <version>${lombok.version}</version>
+                            </path>
+                            <path>
+                                <groupId>org.mapstruct</groupId>
+                                <artifactId>mapstruct-processor</artifactId>
+                                <version>${org.mapstruct.version}</version>
+                            </path>
+                            <path>
+                                <groupId>org.projectlombok</groupId>
+                                <artifactId>lombok-mapstruct-binding</artifactId>
+                                <version>0.2.0</version>
+                            </path>
+                        </annotationProcessorPaths>
+                    </configuration>
+                </plugin>
+            </plugins>
+        </pluginManagement>
+    </build>
+
+    <properties>
+        <org.mapstruct.version>1.5.3.Final</org.mapstruct.version>
+        <maven-surefire-plugin.version>3.0.0-M7</maven-surefire-plugin.version>
+    </properties>
+
+
+</project>

spring-boot-modules/spring-boot-3-test-pitfalls/src/main/java/com/baeldung/sample/pets/PetsApplication.java

@@ -0,0 +1,13 @@
+package com.baeldung.sample.pets;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class PetsApplication {
+
+    public static void main(String[] args) {
+        SpringApplication.run(PetsApplication.class, args);
+    }
+
+}

spring-boot-modules/spring-boot-3-test-pitfalls/src/main/java/com/baeldung/sample/pets/boundary/PetDto.java

@@ -0,0 +1,10 @@
+package com.baeldung.sample.pets.boundary;
+
+import lombok.Data;
+
+@Data
+public class PetDto {
+
+    private String name;
+
+}

spring-boot-modules/spring-boot-3-test-pitfalls/src/main/java/com/baeldung/sample/pets/boundary/PetDtoMapper.java

@@ -0,0 +1,13 @@
+package com.baeldung.sample.pets.boundary;
+
+import com.baeldung.sample.pets.domain.Pet;
+import org.mapstruct.Mapper;
+
+@Mapper(componentModel = "spring")
+public interface PetDtoMapper {
+
+    PetDto map(Pet source);
+
+    Pet map(PetDto source);
+
+}

spring-boot-modules/spring-boot-3-test-pitfalls/src/main/java/com/baeldung/sample/pets/boundary/PetsController.java

@@ -0,0 +1,28 @@
+package com.baeldung.sample.pets.boundary;
+
+import com.baeldung.sample.pets.domain.PetService;
+import lombok.RequiredArgsConstructor;
+import org.springframework.http.MediaType;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+import java.util.Collection;
+import java.util.stream.Collectors;
+
+@RestController
+@RequestMapping("/pets")
+@RequiredArgsConstructor
+public class PetsController {
+
+    private final PetService service;
+    private final PetDtoMapper mapper;
+
+    @GetMapping(produces = MediaType.APPLICATION_JSON_VALUE)
+    public Collection<PetDto> readAll() {
+        return service.getPets().stream()
+          .map(mapper::map)
+          .collect(Collectors.toList());
+    }
+
+}

spring-boot-modules/spring-boot-3-test-pitfalls/src/main/java/com/baeldung/sample/pets/domain/Pet.java

@@ -0,0 +1,4 @@
+package com.baeldung.sample.pets.domain;
+
+public record Pet(String name) {
+}

spring-boot-modules/spring-boot-3-test-pitfalls/src/main/java/com/baeldung/sample/pets/domain/PetService.java

@@ -0,0 +1,14 @@
+package com.baeldung.sample.pets.domain;
+
+import lombok.RequiredArgsConstructor;
+import lombok.experimental.Delegate;
+import org.springframework.stereotype.Service;
+
+@Service
+@RequiredArgsConstructor
+public class PetService {
+
+    @Delegate
+    private final PetServiceRepository repo;
+
+}

spring-boot-modules/spring-boot-3-test-pitfalls/src/main/java/com/baeldung/sample/pets/domain/PetServiceRepository.java

@@ -0,0 +1,13 @@
+package com.baeldung.sample.pets.domain;
+
+import java.util.Collection;
+
+public interface PetServiceRepository {
+
+    boolean add(Pet pet);
+
+    void clear();
+
+    Collection<Pet> getPets();
+
+}

spring-boot-modules/spring-boot-3-test-pitfalls/src/main/java/com/baeldung/sample/pets/domain/PetServiceRepositoryImpl.java

@@ -0,0 +1,29 @@
+package com.baeldung.sample.pets.domain;
+
+import org.springframework.stereotype.Component;
+
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+@Component
+public class PetServiceRepositoryImpl implements PetServiceRepository {
+
+    private final Set<Pet> pets = new HashSet<>();
+
+    @Override
+    public Set<Pet> getPets() {
+        return Collections.unmodifiableSet(pets);
+    }
+
+    @Override
+    public boolean add(Pet pet) {
+        return this.pets.add(pet);
+    }
+
+    @Override
+    public void clear() {
+        this.pets.clear();
+    }
+
+}

spring-boot-modules/spring-boot-3-test-pitfalls/src/main/resources/application.yml

@@ -0,0 +1 @@
+

spring-boot-modules/spring-boot-3-test-pitfalls/src/test/java/com/baeldung/sample/pets/boundary/PetDtoMapperIntegrationTest.java

@@ -0,0 +1,47 @@
+package com.baeldung.sample.pets.boundary;
+
+import com.baeldung.sample.pets.domain.PetService;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.mock.mockito.MockReset;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.ComponentScan;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+
+@ExtendWith(SpringExtension.class)
+public class PetDtoMapperIntegrationTest {
+
+    @Configuration
+    @ComponentScan(basePackageClasses = PetDtoMapper.class)
+    static class PetDtoMapperTestConfig {
+
+        /*
+         * This would be necessary because the controller is also initialized
+         * and needs the service, although we do not want to test it here.
+         *
+         * Solutions:
+         *  - place the mapper into a separate sub package
+         *  - do not test the mapper separately, test it integrated within the controller
+         *    (recommended)
+         */
+        @Bean
+        PetService createServiceMock() {
+            return mock(PetService.class, MockReset.withSettings(MockReset.AFTER));
+        }
+
+    }
+
+    @Autowired
+    PetDtoMapper mapper;
+
+    @Test
+    void shouldExist() { // simply test correct test setup
+        assertThat(mapper).isNotNull();
+    }
+
+}

spring-boot-modules/spring-boot-3-test-pitfalls/src/test/java/com/baeldung/sample/pets/boundary/PetsBoundaryLayer.java

@@ -0,0 +1,10 @@
+package com.baeldung.sample.pets.boundary;
+
+import org.springframework.context.annotation.ComponentScan;
+
+/**
+ * Just an interface to use for compiler-checked component scanning during tests.
+ * @see ComponentScan#basePackageClasses()
+ */
+public interface PetsBoundaryLayer {
+}

spring-boot-modules/spring-boot-3-test-pitfalls/src/test/java/com/baeldung/sample/pets/boundary/PetsControllerMvcIntegrationTest.java

@@ -0,0 +1,36 @@
+package com.baeldung.sample.pets.boundary;
+
+import com.baeldung.sample.pets.domain.PetService;
+import com.baeldung.sample.test.slices.PetsBoundaryTest;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.MediaType;
+import org.springframework.test.web.servlet.MockMvc;
+
+import java.util.Collections;
+
+import static org.mockito.Mockito.when;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+@PetsBoundaryTest
+class PetsControllerMvcIntegrationTest {
+
+    @Autowired
+    MockMvc mvc;
+    @Autowired
+    PetService service;
+
+    @Test
+    void shouldReturnEmptyArrayWhenGetPets() throws Exception {
+        when(service.getPets()).thenReturn(Collections.emptyList());
+        mvc.perform(
+            get("/pets")
+              .accept(MediaType.APPLICATION_JSON)
+          )
+          .andExpect(status().isOk())
+          .andExpect(content().string("[]"));
+    }
+
+}

spring-boot-modules/spring-boot-3-test-pitfalls/src/test/java/com/baeldung/sample/pets/domain/PetServiceIntegrationTest.java

@@ -0,0 +1,26 @@
+package com.baeldung.sample.pets.domain;
+
+import com.baeldung.sample.test.slices.PetsDomainTest;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.when;
+
+@PetsDomainTest
+class PetServiceIntegrationTest {
+
+    @Autowired
+    PetService service;
+    @Autowired // Mock
+    PetServiceRepository repository;
+
+    @Test
+    void shouldAddPetWhenNotAlreadyExisting() {
+        var pet = new Pet("Dog");
+        when(repository.add(pet)).thenReturn(true);
+        var result = service.add(pet);
+        assertThat(result).isTrue();
+    }
+
+}

spring-boot-modules/spring-boot-3-test-pitfalls/src/test/java/com/baeldung/sample/pets/domain/PetServiceUnitTest.java

@@ -0,0 +1,31 @@
+package com.baeldung.sample.pets.domain;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class PetServiceUnitTest {
+
+    PetService service = new PetService(new PetServiceRepositoryImpl());
+
+    @Test
+    void shouldAddPetWhenNotAlreadyExisting() {
+        var pet = new Pet("Dog");
+        var result = service.add(pet);
+        assertThat(result).isTrue();
+        assertThat(service.getPets()).hasSize(1);
+    }
+
+    @Test
+    void shouldNotAddPetWhenAlreadyExisting() {
+        var pet = new Pet("Cat");
+        var result = service.add(pet);
+        assertThat(result).isTrue();
+        // try a second time
+        result = service.add(pet);
+        assertThat(result).isFalse();
+        assertThat(service.getPets()).hasSize(1);
+    }
+
+
+}

spring-boot-modules/spring-boot-3-test-pitfalls/src/test/java/com/baeldung/sample/pets/domain/PetsDomainLayer.java

@@ -0,0 +1,10 @@
+package com.baeldung.sample.pets.domain;
+
+import org.springframework.context.annotation.ComponentScan;
+
+/**
+ * Just an interface to use for compiler-checked component scanning during tests.
+ * @see ComponentScan#basePackageClasses()
+ */
+public interface PetsDomainLayer {
+}

spring-boot-modules/spring-boot-3-test-pitfalls/src/test/java/com/baeldung/sample/test/slices/PetsBoundaryTest.java

@@ -0,0 +1,52 @@
+package com.baeldung.sample.test.slices;
+
+import com.baeldung.sample.pets.boundary.PetsBoundaryLayer;
+import com.baeldung.sample.pets.boundary.PetsController;
+import com.baeldung.sample.pets.domain.PetService;
+import org.junit.jupiter.api.Tag;
+import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
+import org.springframework.boot.test.context.TestConfiguration;
+import org.springframework.boot.test.mock.mockito.MockReset;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.ComponentScan;
+import org.springframework.context.annotation.Import;
+import org.springframework.context.annotation.Primary;
+import org.springframework.test.context.ActiveProfiles;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Inherited;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import static org.mockito.Mockito.mock;
+
+@Documented
+@Inherited
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.TYPE)
+@WebMvcTest(controllers = PetsController.class)
+@ComponentScan(basePackageClasses = PetsBoundaryLayer.class)
+@Import(PetsBoundaryTest.PetBoundaryTestConfiguration.class)
+// further features that can help to configure and execute tests
+@ActiveProfiles({ "test", "boundary-test" })
+@Tag("integration-test")
+@Tag("boundary-test")
+public @interface PetsBoundaryTest {
+
+    @TestConfiguration
+    class PetBoundaryTestConfiguration {
+
+        @Primary
+        @Bean
+        PetService createPetServiceMock() {
+            return mock(
+              PetService.class,
+              MockReset.withSettings(MockReset.AFTER)
+            );
+        }
+
+    }
+
+}

spring-boot-modules/spring-boot-3-test-pitfalls/src/test/java/com/baeldung/sample/test/slices/PetsDomainTest.java

@@ -0,0 +1,52 @@
+package com.baeldung.sample.test.slices;
+
+import com.baeldung.sample.pets.domain.PetServiceRepository;
+import com.baeldung.sample.pets.domain.PetsDomainLayer;
+import org.junit.jupiter.api.Tag;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.boot.test.context.TestConfiguration;
+import org.springframework.boot.test.mock.mockito.MockReset;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.ComponentScan;
+import org.springframework.context.annotation.Import;
+import org.springframework.context.annotation.Primary;
+import org.springframework.test.context.ActiveProfiles;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Inherited;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import static org.mockito.Mockito.mock;
+
+@Documented
+@Inherited
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.TYPE)
+@ExtendWith(SpringExtension.class)
+@ComponentScan(basePackageClasses = PetsDomainLayer.class)
+@Import(PetsDomainTest.PetServiceTestConfiguration.class)
+// further features that can help to configure and execute tests
+@ActiveProfiles({"test", "domain-test"})
+@Tag("integration-test")
+@Tag("domain-test")
+public @interface PetsDomainTest {
+
+    @TestConfiguration
+    class PetServiceTestConfiguration {
+
+        @Primary
+        @Bean
+        PetServiceRepository createPetsRepositoryMock() {
+            return mock(
+              PetServiceRepository.class,
+              MockReset.withSettings(MockReset.AFTER)
+            );
+        }
+
+    }
+
+}

spring-boot-modules/spring-boot-3-test-pitfalls/src/test/resources/application-test.yml

@@ -0,0 +1,11 @@
+logging:
+  level:
+    root: info
+    org:
+      springframework:
+        test:
+          context:
+            cache: DEBUG
+spring:
+  main:
+    allow-bean-definition-overriding: true