Marking Tests as Ignored:

• JUnit 4 uses @Ignore
• JUnit 5 uses @Disabled

Assertions are statically accessed from:

• JUnit 4 uses Assert.
• JUnit 5 uses Assertions.

Assertion message position differs:

• JUnit 4 assertion messages are the first argument
• JUnit 5 assertion messages are the last argument

Annotations for running code before and after each method:

• JUnit 4 uses @Before, and @After
• JUnit 5 uses @BeforeEach, and @AfterEach

Annotations for running code before and after each class:

• JUnit 4 uses @BeforeClass, and @AfterClass
• JUnit 5 uses @BeforeAll, and @AfterAll

By default the methods need to be static in both JUnit 4 and 5, but in v5 we can annotate the class to avoid need to make the All methods static:

• @TestInstance(TestInstance.Lifecycle.PER_CLASS)

Checking that an exception is thrown:

• JUnit 4 uses @Test(expected = InterruptedException.class)
• JUnit 5 uses an assertion with the code in a closure lambda expression, which allows additional assertions to be made on the exception

Exception exception = Assertions.assertThrows(RuntimeException.class, () -> {
    throw new NullPointerException("We interrupt this test to throw an runtime exception");
});

JUnit 4 needs Test Classes and methods to have public visibility:

public class JUnit4Test {
    @Test
    public void aTestMethodAssertingTrue(){
        Assert.assertTrue(true);
    }
}

JUnit 5 does not, so it may make sense to default to package visibility:

class JUnit5Test {
    @Test
    void aTestMethodAssertingTrue(){
        Assertions.assertTrue(true);
    }
}