JUnit: using constructor instead of @Before

Question

I\'m using JUnit 4. I can\'t see the difference between initializing in the constructor or using a dedicated init function annotated by @Before. Does this mean

Answer 1

I prefer to use constructors to initialize my test objects because it allows me to make all the members final so that the IDE or compiler will tell me when the constructor forgot to initialize a member and prevent another method from setting them.

IMHO, @Before violates one of the most important Java conventions, that of relying on the constructor to completely initalize objects!

JUnit 5 also has better support for constructor injection.

Answer 2

There is one thing that constructor can archive but not @Before.

You have to use a constructor when you need to initial fields defined in parent class. For example:

abstract class AbstractIT {
   int fieldAssignedInSubClass;
   public AbstractIT(int fieldAssignedInSubClass) {
      this.fieldAssignedInSubClass= fieldAssignedInSubClass;
   }

   @Before
   void before() {
      // comsume fieldAssignedInSubClass
   } 
}

public class ChildIT extends AbstractIT{
   public ChildIT() {
      // assign fieldAssignedInSubClass by constructor
      super(5566); 
   }

   @Before
   void before() {
      // you cannot assign fieldAssignedInSubClass by a @Before method
   } 
}