Running JUnit 3 tests with JUnit Vintage engine

Question

In our project we have quite a few JUnit 3 tests looking like:

@RunWith(AllTests.class)
public class JUnit3Test extends TestCase {

    public static TestSuite suite()
    {
        var suite = new TestSuite("JUnit 3 style test suite");
        suite.addTest(new JUnit3Test("JUnit 3 style test") {
            @Override
            protected void runTest() {
                testSomething();
            }
        });
        return suite;
    }

    public void testSomething() {
        ...
    }

    ...
}

Currently, we're executing them using JUnit 4, but I'm trying to move to JUnit 5. When I change to useJUnitPlatform() in the Gradle build file these tests are no longer executed.

There's a full working example in https://github.com/ulrikls/junit-vintage-alltests

Any of these changes will successfully execute the JUnit 3 test:

• Switching to JUnit 4 - useJUnit() instead of useJUnitPlatform().
• Changing the name of the test from JUnit 3 style test to testSomeLibraryMethodReturnsTrue.
• Removing the @RunWith(AllTests.class) annotation and the suite() method.

I don't know if this example is even supposed to work in JUnit 5, there doesn't seem to be a lot of documentation on running JUnit 3 tests with JUnit 5. But migrating all our JUnit 3 tests is also not trivial, as the tests do various stuff in the suite() method.