Question: I am using Eclipse Oxygen.3 Release (4.7.3). The following is my JUnit test class:

```java
import static org.junit.Assert.assertEquals;

import org.junit.After;
import org.junit.AfterClass;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;

class MyMathTest {
    MyMath myMath = new MyMath();

    @Before
    public void before() {
        System.out.println("Before");
    }

    @After
    public void after() {
        System.out.println("After");
    }

    @Test
    public void testSum_with3numbers() {
        System.out.println("Test1");
        int result = myMath.sum(new int[] {1,2,3});
        int expected = 6;
        assertEquals(expected, result);
    }

    @Test
    public void testSum_with1numbers() {
        System.out.println("Test2");
        int result = myMath.sum(new int[] {3});
        int expected = 3;
        assertEquals(expected, result);
    }

    @BeforeClass
    public static void beforeClass() {
        System.out.println("Before class");
    }

    @AfterClass
    public static void afterClass() {
        System.out.println("After class");
    }

}

```

When I run this Junit test, eclipse keeps popping up dialog telling **"No tests found with test runner 'JUnit 5'"**. Why?

[![enter image description here](https://i.stack.imgur.com/p7I9T.png)](https://i.stack.imgur.com/p7I9T.png)

Answer: 
You are using JUnit 4 annotations with JUnit 5 dependencies.  

If you want to use JUnit 5 you should replace:  

```
@Before with @BeforeEach
@After with @AfterEach
@BeforeClass with @BeforeAll
@AfterClass with @AfterAll
@Ignore with @Disabled

```

Here is more about JUnit 5 annotations <https://junit.org/junit5/docs/current/user-guide/#writing-tests-annotations/>
My issue was that, Run works fine, debug throws this error. 

I was getting this merely because of low memory in the system. Ideally, eclipse couldn't launch the debug session due to low memory in the system. Error message thrown is confusing. 

Hope it helps someone!