JUnit 中这两个版本的代码有什么区别？

Question

What is the difference between the code in Junit:

class MethodsTest {
    Methods methods = new Methods();
}

and these:

class MethodsTest {

    Methods methods;
    @BeforeEach
    void init() {
        methods = new Methods();
    }
}

When to use first code and when to use second code?

Answer 1

In the first version, you hope that the particular test runner you're using is creating a new instance of MethodsTest implicitly creating a new instance of Methods when executing a particluar test. In the second version, you're telling the test runner you're using explicitly to create a new instance of Methods when executing a new test.

Answer 2

If there is no inheritance involved, there is no difference.

If you were to extend the MethodsTest class, you could override the init() method, and the overriding method would not necessarily either initialize the field directly, or perhaps indirectly by invoking super.init() ; or it could initialize it differently.

Personally, I would prefer the first. It's more concise, not overrideable, and its semantics are obvious to anybody familiar with Java, even without JUnit-specific knowledge.