Spring Boot Unit Test Annotations with Junit 5 -Service Layer -doReturn , whenReturn , @Before, @Spy

This article is all about unit test by using junit for service layer. I explained the controller layer unit test in my first article. You can see the following link, if you need.

Spring Boot Unit Test Annotations with Junit 5 -Controller

I will explain all method about unit test that is used in my code . Let’s get started.

Firstly, I want to show you some differences about methods that look as if they are same.

Mockito: doReturn vs thenReturn

These methods specify what to return when a method is called. In most cases , when-thenReturn is preferred because of readability. However, they have some differences

• doReturn is not type safety.Unlike the doReturn , thenReturn checks method return types and if there is an unsafe type , it raises compile error.
• doReturn is no side effect. This is an advantage, although there is no type safety. If you use spied object that is annotated with @Spy doReturn doesn’t call the method at all .
• thenReturn calls the real method and you need to handle exceptional case, you need to mock the throw maybe.
• If there is no side effect you can use thenReturn for a spied object, although this can be risky . You need to be sure about that :)

What about Spy ?

A spy in mockito is a partial mock. So If you use objects methods , it is a real method invocation for spied object. So as i mentioned above , this can cause some side effects

This link is good explanation about their differences and you can see the usage of doReturn in the example of that article.

Difference between Spy and Mock in Mockito - JavaPointers

@BeforeEach vs @BeforeAll

Lastly, I want to tell you about @BeforeEach and @BeforeAll annotations. The method annotated with @BeforeEach is executed before each test , as it is name signifies :) . On the other side , @BeforeAll annotation provides runs once before the entire test class.

Generally , if multiple tests share same code you can use @BeforeAll (in Junit 4 @BeforeClass) .Establishing database connection can be example for this annotation. You can do some object initializations in the method that is annotated with @BeforeEach (in Junit 4 @Before ) , as you can see in my example code.

In addition , you can think same logic for @AfterEach and @AfterAll. This time , these method runs after the test execution :)

Conclusion

I explained the main differences about some unit test metrics that can cause some troubleshoots when we don’t know what exactly they mean ,as much as I can. I hope that will helpful for you.

Thank you for your reading :)