Testing SpringBoot Applications

SpringBoot is the most popular tech stack for building Java based REST APIs.
In this tutorial, we will learn how to write tests for SpringBoot applications.

• Create SpringBoot Application
• Unit Testing using JUnit 5 and Mockito
• Integration Testing using TestContainers
• Testing MicroService Integrations using MockServer

As we all know, we write unit tests for testing a single component (a class) behaviour
whereas we write integration tests for testing a feature which may involve interaction with multiple components.

Most of the times one component will depend on other components, so while implementing unit tests we should mock
the dependencies with the desired behaviour using frameworks like Mockito.

So, the question is how do we implement Unit Tests and Integration tests in SpringBoot application? Read on :-)

Sample application Code for this article can be found at https://github.com/sivaprasadreddy/spring-boot-tutorials/tree/master/testing/springboot-testing-demo

Create SpringBoot Application

Let us consider a scenario where we are building a REST API to manage users.
If we follow typical 3-tier layered architecture we might have JPA entity User, Spring Data JPA Repository UserRepository,
UserService and UserController implementing CRUD operations as follows:

First of all, create a SpringBoot application with the following dependencies:

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/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.sivalabs</groupId>
    <artifactId>springboot-testing-demo</artifactId>
    <packaging>jar</packaging>
    <version>1.0-SNAPSHOT</version>
    <name>springboot-testing-demo</name>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.8.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
    </properties>

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

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <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.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <scope>runtime</scope>
        </dependency>
    </dependencies>
</project>

By default spring-boot-starter-test comes with JUnit 4 as the testing framework.
We can exclude JUnit4 and add JUnit 5 dependencies as follows:

<dependencies>
    <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.junit.jupiter</groupId>
        <artifactId>junit-jupiter-engine</artifactId>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.junit.jupiter</groupId>
        <artifactId>junit-jupiter-params</artifactId>
        <scope>test</scope>
    </dependency>
</dependencies>

Let us create JPA entity, repository, service and controller for User as follows:

User.java

package com.sivalabs.myservice.entities;

import lombok.*;
import javax.persistence.*;
import javax.validation.constraints.NotEmpty;
import java.io.Serializable;

@Entity
@Table(name = "users")
@Setter
@Getter
@NoArgsConstructor
@AllArgsConstructor
public class User implements Serializable
{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @NotEmpty(message = "Email should not be empty")
    @Column(nullable = false, unique = true, length = 100)
    private String email;

    @Column(nullable = false, length = 100)
    private String password;

    @Column(nullable = false, length = 100)
    private String name;

}

UserRepository.java

package com.sivalabs.myservice.repositories;

import org.springframework.data.jpa.repository.JpaRepository;
import com.sivalabs.myservice.entities.User;
import org.springframework.data.jpa.repository.Query;
import java.util.Optional;

public interface UserRepository extends JpaRepository<User, Long>
{
    @Query("select u from User u where u.email=?1 and u.password=?2")
    Optional<User> login(String email, String password);

    Optional<User> findByEmail(String email);
}

UserService.java

package com.sivalabs.myservice.services;

import com.sivalabs.myservice.exception.UserRegistrationException;
import com.sivalabs.myservice.repositories.UserRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import com.sivalabs.myservice.entities.User;
import java.util.List;
import java.util.Optional;

@Service
@Transactional
public class UserService 
{
    private final UserRepository userRepository;

    @Autowired
    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public Optional<User> login(String email, String password)
    {
        return userRepository.login(email, password);
    }

    public User createUser(User user)
    {
        Optional<User> userOptional = userRepository.findByEmail(user.getEmail());
        if(userOptional.isPresent()){
            throw new UserRegistrationException("User with email "+ user.getEmail()+" already exists");
        }
        return userRepository.save(user);
    }

    public User updateUser(User user)
    {
        return userRepository.save(user);
    }

    public List<User> findAllUsers() {
        return userRepository.findAll();
    }

    public Optional<User> findUserById(Long id) {
        return userRepository.findById(id);
    }

    public void deleteUserById(Long id) {
        userRepository.deleteById(id);
    }

}

UserController.java

package com.sivalabs.myservice.web.controllers;

import com.sivalabs.myservice.entities.User;
import com.sivalabs.myservice.services.UserService;
import lombok.extern.slf4j.Slf4j;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.validation.annotation.Validated;
import org.springframework.web.bind.annotation.*;
import java.util.List;

@RestController
@RequestMapping("/api/users")
@Slf4j
public class UserController {

    private final UserService userService;

    public UserController(UserService userService) {
        this.userService = userService;
    }

    @GetMapping
    public List<User> getAllUsers() {
        return userService.findAllUsers();
    }

    @GetMapping("/{id}")
    public ResponseEntity<User> getUserById(@PathVariable Long id) {
        return userService.findUserById(id)
                .map(ResponseEntity::ok)
                .orElseGet(() -> ResponseEntity.notFound().build());
    }

    @PostMapping
    @ResponseStatus(HttpStatus.CREATED)
    public User createUser(@RequestBody @Validated User user) {
        return userService.createUser(user);
    }

    @PutMapping("/{id}")
    public ResponseEntity<User> updateUser(@PathVariable Long id, @RequestBody User user) {
        return userService.findUserById(id)
                .map(userObj -> {
                    user.setId(id);
                    return ResponseEntity.ok(userService.updateUser(user));
                })
                .orElseGet(() -> ResponseEntity.notFound().build());

    }

    @DeleteMapping("/{id}")
    public ResponseEntity<User> deleteUser(@PathVariable Long id) {
        return userService.findUserById(id)
                .map(user -> {
                    userService.deleteUserById(id);
                    return ResponseEntity.ok(user);
                })
                .orElseGet(() -> ResponseEntity.notFound().build());
    }
}

Nothing too fancy here, typical CRUD operations in SpringBoot application.

ExceptionHandling using Zalando Problem Web

We are going to use Zalando Problem Web SpringBoot starter to handle
Exceptions so that it will automatically convert the application errors into JSON responses.

Just adding the following dependency is enough to start using Zalando Problem Web, and of course, you can customize it if you want to.

<problem-spring-web.version>0.25.0</problem-spring-web.version>
...
...
<dependency>
    <groupId>org.zalando</groupId>
    <artifactId>problem-spring-web-starter</artifactId>
    <version>${problem-spring-web.version}</version>
    <type>pom</type>
</dependency>

Now let us see how we can write Unit Tests and Integration Tests for this functionality.

Unit Testing using JUnit 5 and Mockito

Let us start writing unit tests for UserService.
We should be able to write unit tests for UserService WITHOUT using any Spring features.

We are going to create a mock UserRepository using Mockito.mock() and create UserService instance using the mock UserRepository instance.

package com.sivalabs.myservice.services;

import com.sivalabs.myservice.entities.User;
import com.sivalabs.myservice.exception.UserRegistrationException;
import com.sivalabs.myservice.repositories.UserRepository;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

import java.util.Optional;

import static org.assertj.core.api.Assertions.assertThat;
import static org.junit.jupiter.api.Assertions.assertThrows;
import static org.mockito.ArgumentMatchers.any;
import static org.mockito.BDDMockito.given;
import static org.mockito.Mockito.*;

class UserServiceTest {

    private UserService userService;
    private UserRepository userRepository;

    @BeforeEach
    void setUp() {
        userRepository = mock(UserRepository.class);
        userService = new UserService(userRepository);
    }

    @Test
    void shouldSavedUserSuccessfully() {
        User user = new User(null, "[e-mail]","siva","Siva");
        given(userRepository.findByEmail(user.getEmail())).willReturn(Optional.empty());
        given(userRepository.save(user)).willAnswer(invocation -> invocation.getArgument(0));

        User savedUser = userService.createUser(user);

        assertThat(savedUser).isNotNull();

        verify(userRepository).save(any(User.class));
    }

    @Test
    void shouldThrowErrorWhenSaveUserWithExistingEmail() {
        User user = new User(1L, "[e-mail]","siva","Siva");
        given(userRepository.findByEmail(user.getEmail())).willReturn(Optional.of(user));

        assertThrows(UserRegistrationException.class, () -> {
            userService.createUser(user);
        });

        verify(userRepository, never()).save(any(User.class));
    }
}

I have created UserRepository mock object and UserService instance in @BeforeEach method so that every test has a clean setup.
Here we are not using any Spring or SpringBoot testing features such as @SpringBootTest because we don't have to for testing the behaviour of UserService.

I am not going to write tests for other methods because they are simply delegating the calls to UserRepository.

If you prefer to use annotations magic to create mock UserRepository and inject that mock into UserService,
you can use mockito-junit-jupiter as follows:

Add mockito-junit-jupiter dependency

<dependency>
    <groupId>org.mockito</groupId>
    <artifactId>mockito-junit-jupiter</artifactId>
    <scope>test</scope>
</dependency>

Use @Mock and @InjectMocks to create and inject mock objects as follows:

import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;

@ExtendWith(MockitoExtension.class)
class UserServiceAnnotatedTest {

    @Mock
    private UserRepository userRepository;

    @InjectMocks
    private UserService userService;

    ...
    ...
}

Now, shall we write tests for UserRepository? hmmmm...

The UserRepository is an interface extending JpaRepository and there is hardly any logic we implemented and
we shouldn't be testing Spring Data JPA framework as I strongly believe Spring Data JPA team already tested it :-)

However, we added a couple of custom methods, one leveraging Query naming convention findByEmail() and another with custom JPQL query login().
We should test these methods. If there are any syntactic errors Spring Data JPA throw errors on startup but we should test the logical errors by ourselves.

We could implement tests for UserRepository using SpringBoot's @DataJpaTest annotation with In-memory database support.
But running tests against in-memory database might give a false impression that it will also work on real production database as well.
So, I prefer to run tests against the production database type, in our case Postgresql.

We can use TestContainers support to spin up a postgresql docker container and run the tests pointing to that database.
However, I consider this as an Integration Test rather than Unit Test as we are talking to a real database.
So, we will see how to write Integration tests for UserRepository later.

What about unit tests for Controller?

Yes, I want to write unit tests for controller and I want to check whether the REST endpoint is giving the proper
HTTP ResponseCode or not, returning the expected JSON or not etc.

SpringBoot provides @WebMvcTest annotation to test Spring MVC Controllers.
Also, @WebMvcTest based tests run faster as it will load only the specified controller and its dependencies only without loading the entire application.

While loading the Controller using @WebMvcTest SpringBoot won't automatically load Zalando Problem Web AutoConfiguration.
So, we need to configure ControllerAdvice as follows:

package com.sivalabs.myservice.common;

import org.springframework.context.annotation.Profile;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.zalando.problem.spring.web.advice.ProblemHandling;

@Profile("test")
@ControllerAdvice
public final class ExceptionHandling implements ProblemHandling {

}

Now we can write tests for UserController by injecting a Mock UserService bean and invoke API endpoints using MockMvc.

As SpringBoot is creating the UserController instance we are creating mock UserService bean using Spring's @MockBean as opposed to plain Mockito's @Mock.

package com.sivalabs.myservice.web.controllers;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.sivalabs.myservice.entities.User;
import com.sivalabs.myservice.services.UserService;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
import org.springframework.boot.test.mock.mockito.MockBean;
import org.springframework.http.MediaType;
import org.springframework.test.context.ActiveProfiles;
import org.springframework.test.web.servlet.MockMvc;
import org.zalando.problem.ProblemModule;
import org.zalando.problem.violations.ConstraintViolationProblemModule;

import java.util.ArrayList;
import java.util.List;
import java.util.Optional;

import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.Matchers.hasSize;
import static org.mockito.ArgumentMatchers.any;
import static org.mockito.BDDMockito.given;
import static org.mockito.Mockito.doNothing;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;

@WebMvcTest(controllers = UserController.class)
@ActiveProfiles("test")
class UserControllerTest {

    @Autowired
    private MockMvc mockMvc;

    @MockBean
    private UserService userService;

    @Autowired
    private ObjectMapper objectMapper;

    private List<User> userList;

    @BeforeEach
    void setUp() {
        this.userList = new ArrayList<>();
        this.userList.add(new User(1L, "[e-mail]", "pwd1","User1"));
        this.userList.add(new User(2L, "[e-mail]", "pwd2","User2"));
        this.userList.add(new User(3L, "[e-mail]", "pwd3","User3"));

        objectMapper.registerModule(new ProblemModule());
        objectMapper.registerModule(new ConstraintViolationProblemModule());
    }

    @Test
    void shouldFetchAllUsers() throws Exception {
        given(userService.findAllUsers()).willReturn(this.userList);

        this.mockMvc.perform(get("/api/users"))
                .andExpect(status().isOk())
                .andExpect(jsonPath("$.size()", is(userList.size())));
    }

    @Test
    void shouldFindUserById() throws Exception {
        Long userId = 1L;
        User user = new User(userId, "[e-mail]", "pwd", "Name");
        given(userService.findUserById(userId)).willReturn(Optional.of(user));

        this.mockMvc.perform(get("/api/users/{id}", userId))
                .andExpect(status().isOk())
                .andExpect(jsonPath("$.email", is(user.getEmail())))
                .andExpect(jsonPath("$.password", is(user.getPassword())))
                .andExpect(jsonPath("$.name", is(user.getName())))
        ;
    }

    @Test
    void shouldReturn404WhenFetchingNonExistingUser() throws Exception {
        Long userId = 1L;
        given(userService.findUserById(userId)).willReturn(Optional.empty());

        this.mockMvc.perform(get("/api/users/{id}", userId))
                .andExpect(status().isNotFound());

    }

    @Test
    void shouldCreateNewUser() throws Exception {
        given(userService.createUser(any(User.class))).willAnswer((invocation) -> invocation.getArgument(0));

        User user = new User(null, "[e-mail]", "pwd", "Name");
        this.mockMvc.perform(post("/api/users")
                .contentType(MediaType.APPLICATION_JSON_UTF8)
                .content(objectMapper.writeValueAsString(user)))
                .andExpect(status().isCreated())
                .andExpect(jsonPath("$.email", is(user.getEmail())))
                .andExpect(jsonPath("$.password", is(user.getPassword())))
                .andExpect(jsonPath("$.name", is(user.getName())))
                ;

    }

    @Test
    void shouldReturn400WhenCreateNewUserWithoutEmail() throws Exception {
        User user = new User(null, null, "pwd", "Name");

        this.mockMvc.perform(post("/api/users")
                .contentType(MediaType.APPLICATION_JSON_UTF8)
                .content(objectMapper.writeValueAsString(user)))
                .andExpect(status().isBadRequest())
                .andExpect(header().string("Content-Type", is("application/problem+json")))
                .andExpect(jsonPath("$.type", is("https://zalando.github.io/problem/constraint-violation")))
                .andExpect(jsonPath("$.title", is("Constraint Violation")))
                .andExpect(jsonPath("$.status", is(400)))
                .andExpect(jsonPath("$.violations", hasSize(1)))
                .andExpect(jsonPath("$.violations[0].field", is("email")))
                .andExpect(jsonPath("$.violations[0].message", is("Email should not be empty")))
                .andReturn()
        ;
    }

    @Test
    void shouldUpdateUser() throws Exception {
        Long userId = 1L;
        User user = new User(userId, "[e-mail]", "pwd", "Name");
        given(userService.findUserById(userId)).willReturn(Optional.of(user));
        given(userService.updateUser(any(User.class))).willAnswer((invocation) -> invocation.getArgument(0));

        this.mockMvc.perform(put("/api/users/{id}", user.getId())
                .contentType(MediaType.APPLICATION_JSON_UTF8)
                .content(objectMapper.writeValueAsString(user)))
                .andExpect(status().isOk())
                .andExpect(jsonPath("$.email", is(user.getEmail())))
                .andExpect(jsonPath("$.password", is(user.getPassword())))
                .andExpect(jsonPath("$.name", is(user.getName())));

    }

    @Test
    void shouldReturn404WhenUpdatingNonExistingUser() throws Exception {
        Long userId = 1L;
        given(userService.findUserById(userId)).willReturn(Optional.empty());
        User user = new User(userId, "[e-mail]", "pwd", "Name");

        this.mockMvc.perform(put("/api/users/{id}", userId)
                .contentType(MediaType.APPLICATION_JSON_UTF8)
                .content(objectMapper.writeValueAsString(user)))
                .andExpect(status().isNotFound());

    }

    @Test
    void shouldDeleteUser() throws Exception {
        Long userId = 1L;
        User user = new User(userId, "[e-mail]", "pwd", "Name");
        given(userService.findUserById(userId)).willReturn(Optional.of(user));
        doNothing().when(userService).deleteUserById(user.getId());

        this.mockMvc.perform(delete("/api/users/{id}", user.getId()))
                .andExpect(status().isOk())
                .andExpect(jsonPath("$.email", is(user.getEmail())))
                .andExpect(jsonPath("$.password", is(user.getPassword())))
                .andExpect(jsonPath("$.name", is(user.getName())));

    }

    @Test
    void shouldReturn404WhenDeletingNonExistingUser() throws Exception {
        Long userId = 1L;
        given(userService.findUserById(userId)).willReturn(Optional.empty());

        this.mockMvc.perform(delete("/api/users/{id}", userId))
                .andExpect(status().isNotFound());

    }

}

Now we have a good amount of unit tests testing various components of our application.
But still, there is a lot of chance for things to go wrong, maybe we might have some property configuration issues,
we might have some errors in our DB migration scripts etc.

So, let's write Integration Tests to have more confidence that our application is running properly.

Integration Testing using TestContainer

SpringBoot provides excellent support for integration testing. We can use @SpringBootTest annotation to load the application context and test various components.

Let us start with writing integration tests for UserController.
As I mentioned earlier we want to test using Postgres database instead of an in-memory database.

Add the following dependencies.

<dependency>
    <groupId>org.testcontainers</groupId>
    <artifactId>postgresql</artifactId>
    <version>1.11.3</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.testcontainers</groupId>
    <artifactId>junit-jupiter</artifactId>
    <version>1.11.3</version>
    <scope>test</scope>
</dependency>

We can use TestContainers support for JUnit 5 as mentioned here https://www.testcontainers.org/test_framework_integration/junit_5/.
However, starting and stopping docker containers for every test or every test class might cause tests running slowly.
So, we are going to use Singleton Containers approach mentioned at https://www.testcontainers.org/test_framework_integration/manual_lifecycle_control/#singleton-containers

Let us create a base class AbstractIntegrationTest so that all our integration tests can extend without repeating the common configuration.

package com.sivalabs.myservice.common;

import com.fasterxml.jackson.databind.ObjectMapper;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.util.TestPropertyValues;
import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.test.context.ActiveProfiles;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.web.servlet.MockMvc;
import org.testcontainers.containers.PostgreSQLContainer;

import static org.springframework.boot.test.context.SpringBootTest.WebEnvironment.RANDOM_PORT;

@Slf4j
@ActiveProfiles("test")
@SpringBootTest(webEnvironment = RANDOM_PORT)
@AutoConfigureMockMvc
@ContextConfiguration(initializers = {AbstractIntegrationTest.Initializer.class})
public abstract class AbstractIntegrationTest {

    @Autowired
    protected MockMvc mockMvc;

    @Autowired
    protected ObjectMapper objectMapper;

    private static PostgreSQLContainer sqlContainer;

    static {
        sqlContainer = new PostgreSQLContainer("postgres:10.7")
                .withDatabaseName("integration-tests-db")
                .withUsername("sa")
                .withPassword("sa");
        sqlContainer.start();
    }

    public static class Initializer
            implements ApplicationContextInitializer<ConfigurableApplicationContext> {
        public void initialize(ConfigurableApplicationContext configurableApplicationContext) {
            TestPropertyValues.of(
                    "spring.datasource.url=" + sqlContainer.getJdbcUrl(),
                    "spring.datasource.username=" + sqlContainer.getUsername(),
                    "spring.datasource.password=" + sqlContainer.getPassword()
            ).applyTo(configurableApplicationContext.getEnvironment());
        }
    }

}

We have used @AutoConfigureMockMvc to auto-configure MockMvc,
and @SpringBootTest(webEnvironment = RANDOM_PORT) to start the server on a random available port.

We have started PostgreSQLContainer and used @ContextConfiguration(initializers={AbstractIntegrationTest.Initializer.class})
to configure the dynamic database connection properties.

Now we can implement Integration Test for UserController as follows:

package com.sivalabs.myservice.web.controllers;

import com.sivalabs.myservice.common.AbstractIntegrationTest;
import com.sivalabs.myservice.entities.User;
import com.sivalabs.myservice.repositories.UserRepository;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.MediaType;

import java.util.ArrayList;
import java.util.List;

import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.Matchers.hasSize;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;

class UserControllerIT extends AbstractIntegrationTest {

    @Autowired
    private UserRepository userRepository;

    private List<User> userList = null;

    @BeforeEach
    void setUp() {
        userRepository.deleteAll();

        userList = new ArrayList<>();
        this.userList.add(new User(1L, "[e-mail]", "pwd1","User1"));
        this.userList.add(new User(2L, "[e-mail]", "pwd2","User2"));
        this.userList.add(new User(3L, "[e-mail]", "pwd3","User3"));

        userList = userRepository.saveAll(userList);
    }

    @Test
    void shouldFetchAllUsers() throws Exception {
        this.mockMvc.perform(get("/api/users"))
                .andExpect(status().isOk())
                .andExpect(jsonPath("$.size()", is(userList.size())));
    }

    @Test
    void shouldFindUserById() throws Exception {
        User user = userList.get(0);
        Long userId = user.getId();

        this.mockMvc.perform(get("/api/users/{id}", userId))
                .andExpect(status().isOk())
                .andExpect(jsonPath("$.email", is(user.getEmail())))
                .andExpect(jsonPath("$.password", is(user.getPassword())))
                .andExpect(jsonPath("$.name", is(user.getName())))
        ;
    }

    @Test
    void shouldCreateNewUser() throws Exception {
        User user = new User(null, "[e-mail]", "pwd", "name");
        this.mockMvc.perform(post("/api/users")
                .contentType(MediaType.APPLICATION_JSON_UTF8)
                .content(objectMapper.writeValueAsString(user)))
                .andExpect(status().isCreated())
                .andExpect(jsonPath("$.email", is(user.getEmail())))
                .andExpect(jsonPath("$.password", is(user.getPassword())))
                .andExpect(jsonPath("$.name", is(user.getName())));

    }

    @Test
    void shouldReturn400WhenCreateNewUserWithoutEmail() throws Exception {
        User user = new User(null, null, "pwd", "Name");

        this.mockMvc.perform(post("/api/users")
                .contentType(MediaType.APPLICATION_JSON_UTF8)
                .content(objectMapper.writeValueAsString(user)))
                .andExpect(status().isBadRequest())
                .andExpect(header().string("Content-Type", is("application/problem+json")))
                .andExpect(jsonPath("$.type", is("https://zalando.github.io/problem/constraint-violation")))
                .andExpect(jsonPath("$.title", is("Constraint Violation")))
                .andExpect(jsonPath("$.status", is(400)))
                .andExpect(jsonPath("$.violations", hasSize(1)))
                .andExpect(jsonPath("$.violations[0].field", is("email")))
                .andExpect(jsonPath("$.violations[0].message", is("Email should not be empty")))
                .andReturn()
        ;
    }

    @Test
    void shouldUpdateUser() throws Exception {
        User user = userList.get(0);
        user.setPassword("newpwd");
        user.setName("NewName");

        this.mockMvc.perform(put("/api/users/{id}", user.getId())
                .contentType(MediaType.APPLICATION_JSON_UTF8)
                .content(objectMapper.writeValueAsString(user)))
                .andExpect(status().isOk())
                .andExpect(jsonPath("$.email", is(user.getEmail())))
                .andExpect(jsonPath("$.password", is(user.getPassword())))
                .andExpect(jsonPath("$.name", is(user.getName())));

    }

    @Test
    void shouldDeleteUser() throws Exception {
        User user = userList.get(0);

        this.mockMvc.perform(
                delete("/api/users/{id}", user.getId()))
                .andExpect(status().isOk())
                .andExpect(jsonPath("$.email", is(user.getEmail())))
                .andExpect(jsonPath("$.password", is(user.getPassword())))
                .andExpect(jsonPath("$.name", is(user.getName())));

    }

}

The UserControllerIT tests look very similar to UserControllerTest with the difference being how we load the ApplicationContext.
While using @SpringBootTest SpringBoot will actually start the application by loading the entire application
so that tests will fail if there is any misconfiguration.

Next, we are going to write a test for UserRepository using @DataJpaTest.
But we want to run tests against a real database, not with an in-memory database.
We can use @AutoConfigureTestDatabase(replace=AutoConfigureTestDatabase.Replace.NONE) to turn-off using in-memory database and use the configured database.

Let us create PostgreSQLContainerInitializer so that any repository tests can use this to configure dynamic Postgres database properties.

package com.sivalabs.myservice.common;

import lombok.extern.slf4j.Slf4j;
import org.springframework.boot.test.util.TestPropertyValues;
import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;
import org.testcontainers.containers.PostgreSQLContainer;

@Slf4j
public class PostgreSQLContainerInitializer
        implements ApplicationContextInitializer<ConfigurableApplicationContext> {

    private static PostgreSQLContainer sqlContainer;

    static {
        sqlContainer = new PostgreSQLContainer("postgres:10.7")
                .withDatabaseName("integration-tests-db")
                .withUsername("sa")
                .withPassword("sa");
        sqlContainer.start();
    }

    public void initialize (ConfigurableApplicationContext configurableApplicationContext){
        TestPropertyValues.of(
                "spring.datasource.url=" + sqlContainer.getJdbcUrl(),
                "spring.datasource.username=" + sqlContainer.getUsername(),
                "spring.datasource.password=" + sqlContainer.getPassword()
        ).applyTo(configurableApplicationContext.getEnvironment());
    }

}

Now we can create UserRepositoryTest as follows:

package com.sivalabs.myservice.repositories;

import com.sivalabs.myservice.common.PostgreSQLContainerInitializer;
import com.sivalabs.myservice.entities.User;
import lombok.extern.slf4j.Slf4j;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.jdbc.AutoConfigureTestDatabase;
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
import org.springframework.test.context.ContextConfiguration;
import javax.persistence.EntityManager;
import java.util.Optional;
import static org.assertj.core.api.Assertions.assertThat;

@Slf4j
@DataJpaTest
@AutoConfigureTestDatabase(replace= AutoConfigureTestDatabase.Replace.NONE)
@ContextConfiguration(initializers = {PostgreSQLContainerInitializer.class})
class UserRepositoryTest {

    @Autowired
    EntityManager entityManager;

    @Autowired
    private UserRepository userRepository;

    @Test
    void shouldReturnUserGivenValidCredentials() {
        User user = new User(null, "[e-mail]", "test", "Test");
        entityManager.persist(user);

        Optional<User> userOptional = userRepository.login("[e-mail]", "test");

        assertThat(userOptional).isNotEmpty();
    }
}

Well, I guess we learned something about how to write unit tests and integration tests using various SpringBoot features.

We are living in a Microservices world and there is a high chance that our service might talk to other microservices.
How are we going to test those integration points? How are we going to verify the timeout scenarios?
Well, we can certainly use a Mock object and pray GOD that it will work fine in production :-)
Or we can use libraries like MockServer to simulate the service-to-service communication.

Testing MicroService Integrations using MockServer

Assume from our application we want to fetch GitHub profile of a user. We can use GitHub REST API to fetch the user profile.
Also, we want to timeout the call after 2 seconds and if we don't get a response by that time we want to return a default user response.

We can implement this using Hystrix as follows:

application.properties

githuub.api.base-url=https://api.github.com

package com.sivalabs.myservice.config;

import lombok.Data;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
@Data
public class ApplicationProperties {

    @Value("${githuub.api.base-url}")
    private String githubBaseUrl;
}

Register RestTemplate bean and enable Hystrix CircuitBreaker using @EnableCircuitBreaker.

package com.sivalabs.myservice;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
@EnableCircuitBreaker
public class Application
{
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

Create GithubUser class which holds response from GitHub API.

package com.sivalabs.myservice.model;

import com.fasterxml.jackson.annotation.JsonProperty;
import lombok.Data;

@Data
public class GithubUser {
    private Long id;
    private String login;
    private String url;
    private String name;
    @JsonProperty("public_repos")
    private int publicRepos;
    private int followers;
    private int following;
}

Create GithubService which talks to GitHub REST API using RestTemplate as follows:

package com.sivalabs.myservice.services;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixProperty;
import com.sivalabs.myservice.config.ApplicationProperties;
import com.sivalabs.myservice.model.GithubUser;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

@Service
@Slf4j
public class GithubService {
    private final ApplicationProperties properties;
    private final RestTemplate restTemplate;

    @Autowired
    public GithubService(ApplicationProperties properties, RestTemplate restTemplate) {
        this.properties = properties;
        this.restTemplate = restTemplate;
    }

    @HystrixCommand(fallbackMethod = "getDefaultUser", commandProperties = {
            @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "2000")
    })
    public GithubUser getGithubUserProfile(String username) {
        log.info("GithubBaseUrl:"+properties.getGithubBaseUrl());
        return this.restTemplate.getForObject(properties.getGithubBaseUrl() + "/users/" + username, GithubUser.class);
    }

    GithubUser getDefaultUser(String username) {
        log.info("---------getDefaultUser-----------");
        GithubUser user = new GithubUser();
        user.setId(-1L);
        user.setLogin("guest");
        user.setName("Guest");
        user.setPublicRepos(0);
        return user;
    }
}

Let us create a GithubController with an endpoint to return the users GitHub profile.

package com.sivalabs.myservice.web.controllers;

import com.sivalabs.myservice.model.GithubUser;
import com.sivalabs.myservice.services.GithubService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/api/github")
public class GithubController {

    private final GithubService githubService;

    @Autowired
    public GithubController(GithubService githubService) {
        this.githubService = githubService;
    }

    @GetMapping("/users/{username}")
    public GithubUser getGithubUserProfile(@PathVariable String username) {
        return githubService.getGithubUserProfile(username);
    }
}

We can use MockServer to simulate the dependent microservice responses so that we can verify our application behaviour in various scenarios.

We can use TestContainers support to spin up MockServer docker container as follows:

Add the following dependencies:

<dependency>
    <groupId>org.testcontainers</groupId>
    <artifactId>mockserver</artifactId>
    <version>1.11.3</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.mock-server</groupId>
    <artifactId>mockserver-netty</artifactId>
    <version>5.5.1</version>
    <scope>test</scope>
</dependency>

In AbstractIntegrationTest add MockServerContainer configuration as follows:

import org.mockserver.client.MockServerClient;
import org.testcontainers.containers.MockServerContainer;

@Slf4j
@ActiveProfiles("test")
@SpringBootTest(webEnvironment = RANDOM_PORT)
@AutoConfigureMockMvc
@ContextConfiguration(initializers = {AbstractIntegrationTest.Initializer.class})
public abstract class AbstractIntegrationTest {
    ...
    ...
    private static MockServerContainer mockServerContainer;

    static {
        ....
        ....
        mockServerContainer = new MockServerContainer();
        mockServerContainer.start();
    }

    protected MockServerClient mockServerClient = new MockServerClient(
            mockServerContainer.getContainerIpAddress(),
            mockServerContainer.getServerPort());


    public static class Initializer
            implements ApplicationContextInitializer<ConfigurableApplicationContext> {
        public void initialize(ConfigurableApplicationContext configurableApplicationContext) {
            TestPropertyValues.of(
                    "spring.datasource.url=" + sqlContainer.getJdbcUrl(),
                    "spring.datasource.username=" + sqlContainer.getUsername(),
                    "spring.datasource.password=" + sqlContainer.getPassword(),
                    "githuub.api.base-url=" + mockServerContainer.getEndpoint()
            ).applyTo(configurableApplicationContext.getEnvironment());
        }
    }

}

Note that we are stating MockServerContainer and injecting the endpoint URL with "githuub.api.base-url="+mockServerContainer.getEndpoint().
Also, we have created MockServerClient which we are going to use for setting up expected responses.

package com.sivalabs.myservice.web.controllers;

import com.sivalabs.myservice.common.AbstractIntegrationTest;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.mockserver.model.Header;
import org.mockserver.verify.VerificationTimes;

import java.util.concurrent.TimeUnit;

import static org.hamcrest.CoreMatchers.is;
import static org.mockserver.model.HttpRequest.request;
import static org.mockserver.model.HttpResponse.response;
import static org.mockserver.model.JsonBody.json;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

class GithubControllerIT extends AbstractIntegrationTest {

    @BeforeEach
    void setup() {
        mockServerClient.reset();
    }

    @Test
    void shouldGetGithubUserProfile() throws Exception {
        String username = "sivaprasadreddy";
        mockGetUserFromGithub(username);
        this.mockMvc.perform(get("/api/github/users/{username}", username))
                .andExpect(status().isOk())
                .andExpect(jsonPath("$.login", is(username)))
                .andExpect(jsonPath("$.name", is("K. Siva Prasad Reddy")))
                .andExpect(jsonPath("$.public_repos", is(50)))
                ;
        verifyMockServerRequest("GET", "/users/.*", 1);
    }

    private void mockGetUserFromGithub(String username) {
        mockServerClient.when(
            request().withMethod("GET").withPath("/users/.*"))
            .respond(
                response()
                    .withStatusCode(200)
                    .withHeaders(new Header("Content-Type", "application/json; charset=utf-8"))
                    .withBody(json("{ " +
                            "\"login\": \""+username+"\", " +
                            "\"name\": \"K. Siva Prasad Reddy\", " +
                            "\"public_repos\": 50 " +
                            "}"))
            );
    }

    private void verifyMockServerRequest(String method, String path, int times) {
        mockServerClient.verify(
                request()
                        .withMethod(method)
                        .withPath(path),
                VerificationTimes.exactly(times)
        );
    }
}

Note that we are setting up expected JSON response for <githuub.api.base-url>/users/.* URL pattern on mockServerClient.
So, when we make a call to http://localhost:8080/api/github/users/{username} GithubController will in-turn call GithubService which makes a call to
<githuub.api.base-url>/users/{username} and return the mock JSON response that we set using mockServerClient.

We can also simulate the failures and timeout scenarios as follows:

@Test
void shouldGetDefaultUserProfileWhenFetchingFromGithubFails() throws Exception {
    mockGetUserFromGithubFailure();
    this.mockMvc.perform(get("/api/github/users/{username}", "dummy"))
            .andExpect(status().isOk())
            .andExpect(jsonPath("$.login", is("guest")))
            .andExpect(jsonPath("$.name", is("Guest")))
            .andExpect(jsonPath("$.public_repos", is(0)))
    ;
    verifyMockServerRequest("GET", "/users/.*", 1);
}

@Test
void shouldGetDefaultUserProfileWhenFetchingFromGithubTimeout() throws Exception {
    mockGetUserFromGithubDelayResponse();
    this.mockMvc.perform(get("/api/github/users/{username}", "dummy"))
            .andExpect(status().isOk())
            .andExpect(jsonPath("$.login", is("guest")))
            .andExpect(jsonPath("$.name", is("Guest")))
            .andExpect(jsonPath("$.public_repos", is(0)))
    ;
    verifyMockServerRequest("GET", "/users/.*", 1);
}

private void mockGetUserFromGithubDelayResponse() {
    mockServerClient.when(
        request().withMethod("GET").withPath("/users/.*"))
        .respond(response().withStatusCode(200).withDelay(TimeUnit.SECONDS, 10));
}

private void mockGetUserFromGithubFailure() {
    mockServerClient.when(
        request().withMethod("GET").withPath("/users/.*"))
        .respond(response().withStatusCode(404));
}

In shouldGetDefaultUserProfileWhenFetchingFromGithubFails() test we are setting up the mockServer to respond
with 404 error to verify Hystrix fallback method is working or not.

Similarly, In shouldGetDefaultUserProfileWhenFetchingFromGithubTimeout() test we are setting up the mockServer to respond
with delay of 10 SECONDS to verify whether Hystrix timeout is working or not.

Make sure to reset mockServerClient using mockServerClient.reset() for every test in @BeforeEach method to reset any expectations set in previous test run.

Sample application Code for this article can be found at https://github.com/sivaprasadreddy/spring-boot-tutorials/tree/master/testing/springboot-testing-demo

I hope we have covered many common testing scenarios in SpringBoot applications.

Comments

[Maddy]

Thanks a lot for this! 👏🏾👏🏾👏🏾

[Aishu darsh]

Hi Sir, whether we can write tests for exiting Springboot app? I'm having ExitCodeExceptionMapper in main class. stuck at writing test for different cases and it's exit code(1/2/3).?

[Harshad Wazarkar]

Hi sir,
this is awesome article thank you so much it help a lot

but my application is secure with JWT and i want to perform unit test on controller using junit 5
so how can i mock the security context

[K. Siva Prasad Reddy]

We can use @WithMockUser from Spring Security Testing support for simulating authenticated user flow as described here docs.spring.io/spring-security/sit....

[Harshad Wazarkar]

thank you sir for your replay.

i will try this