Junit @Before not working properly

问题

@Before
public void setup(){
    Ground ground = new Ground(100, 100);
}

@Test
public void getDimX(){
    String msg = "For a newly created Ground(100, 100), ground.getDimensionX()      should return 100";
    assertEquals(100, ground.getDimensionX());
}

The above code returns a NullPointerException. If I move the Ground ground = new Ground(4, 4); into the getDimX() method, the test runs just fine. I have a number of tests that will use the same ground, so I would prefer not to make a new one with each test case. Also, if I get rid of the @Begin block entirely and just leave the ground instantiation, it also works fine. What then is the point of the @Before?

回答1:

created a private field in your test class outside your test setup, i.e.

public class MyTest{
    private Ground ground;
    ...
}

Then instantiate ground in your before()

@Before
public void before(){ground = new Ground(100,100);}

回答2:

I had faced this issue when instead of org.junit.Test I had imported org.junit.jupiter.api.Test

回答3:

Agreeing with @ANU JOHN, the following imports didn't match up:

import org.junit.Before;
import org.junit.jupiter.api.Test;

Changing the second to org.junit.Test; fixed it for me.

来源：https://stackoverflow.com/questions/21612890/junit-before-not-working-properly