Group JUnit Tests with @Nested

I really like the way that I can nest my JavaScript tests using describe blocks. This keeps my tests nicely organized and grouped together in functional blocks which can be super useful when you get a whole lot of tests created.

describe("my component", () => {
    describe("validation", () => {
        it("ensures that user name is provided", () => {
            // test here
        })
        
        it("ensures that password is valid", () => {
            // test here
        })
    })
    
    describe("when saved", () => {
        it("displays an indication that mutation is in progress", () => {
            // test here
        })
        
        it("provides feedback of success", () => {
            // test here
        })
        
        it("provides an error message on failure", () => {
            // test here
        })
    })
})

I was not aware that you can do something like this in Java with JUnit. Reading through Pragmatic Unit Testing in Java with JUnit I found that this functionality is available by making an inner class and using the @Nested annotation.

Note that @Nested is a JUnit 5 feature, so you’ll need to import it:

import org.junit.jupiter.api.Nested;

Here is an example of how the code above might be organized using JUnit and Java:

class MyComponentTest {

    @Nested
    class Validation {

        @Test
        void ensuresThatUserNameIsProvided() {
            // test here
        }

        @Test
        void ensuresThatPasswordIsValid() {
            // test here
        }
    }

    @Nested
    class WhenSaved {

        @Test
        void displaysIndicationThatMutationIsInProgress() {
            // test here
        }

        @Test
        void providesFeedbackOfSuccess() {
            // test here
        }

        @Test
        void providesErrorMessageOnFailure() {
            // test here
        }
    }
}

One nice bonus: each @Nested class can have its own @BeforeEach setup method, so you can share setup logic within a group without affecting other groups.

I enjoy finding ways to make my testing better and easier to use. Do you have a favorite tip that you use to make your tests better organized?