@Before method in TestRule is not called

Question

I implemented a JUnit 4 TestRule (extending an ExternalResource), and injected it as a @ClassRule in my test class: I want to initialize a resource once for all in every test of this class, and tear it down eventually.

My issue is that my @Before and @After rule-methods are not called at all before/after my @Test method: any idea why this is happening?

Minimal compilable example:

package com.acme.test;

import static org.junit.Assert.assertNull;
import org.junit.ClassRule;
import org.junit.Test;
import org.junit.rules.ExternalResource;

class Coffee {
    public void throwAway() {}
}

class CoffeeMachine extends ExternalResource {
    Coffee whatElse;    
    @Override protected void before() throws Throwable {
        whatElse = new Coffee();
    }

    @Override protected void after() {
        whatElse.throwAway();
    }

    public Coffee gimmieCoffee() { return whatElse; }
}

public class CoffeeTester {
    @ClassRule public static CoffeeMachine CM = new CoffeeMachine();

    @Test public void drinkACoffee() {
        Coffee c = CM.gimmieCoffee();
        assertNull(c);  // ---> Coffee is null!!                       (fuuuuuuuuuu...)
    }
}

Is there something I am misunderstanding here? Note that the same happens with a non-static @Rule.

I am using JUnit 4.11.

Thank you very much for any hint.

Answer 1

I think this is a problem with your test runner. Maybe some plugin has installed a custom runner which is used when you run your tests from Ecilpse?

Check the run configuration for your test and make sure that the standard JUnit 4 test runner is used:

Answer 2

I see no issue here, but just a misunderstanding. First of all, let's read assert as it must be and change your code a bit (it is obvious your test says c must not be null which gives us: assertNotNull(c);

I've also added some output in order to show you what is going on. Please try to run it.

package com.acme.test;

import static org.junit.Assert.assertNotNull;
import org.junit.ClassRule;
import org.junit.Test;
import org.junit.rules.ExternalResource;

class Coffee {
    public void throwAway() {}
}

class CoffeeMachine extends ExternalResource {
    Coffee whatElse;    
    @Override protected void before() throws Throwable {
        whatElse = new Coffee();
        System.out.println(" ### executing before: " + whatElse);
    }

    @Override protected void after() {
        whatElse.throwAway();
    }

    public Coffee gimmieCoffee() { return whatElse; }
}

public class CoffeeTester {
    @ClassRule public static CoffeeMachine CM = new CoffeeMachine();

    @Test public void drinkACoffee() {
        Coffee c = CM.gimmieCoffee();
        System.out.println(" ### executing test: " + c);
        assertNotNull(c); 
    }
}

For me it gives the following:

 ### executing before: com.acme.test.Coffee@28f67ac7
[VerboseTestNG] INVOKING: "com.acme.test.CoffeeTester" - com.acme.test.CoffeeTester.drinkACoffee()
 ### executing test: com.acme.test.Coffee@28f67ac7
[VerboseTestNG] PASSED: "com.acme.test.CoffeeTester" - com.acme.test.CoffeeTester.drinkACoffee() finished in 4 ms
[VerboseTestNG] 
[VerboseTestNG] ===============================================
[VerboseTestNG]     com.acme.test.CoffeeTester
[VerboseTestNG]     Tests run: 1, Failures: 0, Skips: 0
[VerboseTestNG] ===============================================

So c is not null as you expect it to be.