How do I assert my exception message with JUnit Test annotation?

You could use the @Rule annotation with ExpectedException, like this:

@Rulepublic ExpectedException expectedEx = ExpectedException.none();@Testpublic void shouldThrowRuntimeExceptionWhenEmployeeIDisNull() throws Exception {    expectedEx.expect(RuntimeException.class);    expectedEx.expectMessage("Employee ID is null");    // do something that should throw the exception...    System.out.println("=======Starting Exception process=======");    throw new NullPointerException("Employee ID is null");}

Note that the example in the ExpectedException docs is (currently) wrong - there's no public constructor, so you have to use ExpectedException.none().

In JUnit 4.13 you can do:

import static org.junit.Assert.assertEquals;import static org.junit.Assert.assertThrows;...@Testvoid exceptionTesting() {  IllegalArgumentException exception = assertThrows(    IllegalArgumentException.class,     () -> { throw new IllegalArgumentException("a message"); }  );  assertEquals("a message", exception.getMessage());}

This also works in JUnit 5 but with different imports:

import static org.junit.jupiter.api.Assertions.assertEquals;import static org.junit.jupiter.api.Assertions.assertThrows;...

I like the @Rule answer. However, if for some reason you don't want to use rules. There is a third option.

@Test (expected = RuntimeException.class)public void myTestMethod(){   try   {      //Run exception throwing operation here   }   catch(RuntimeException re)   {      String message = "Employee ID is null";      assertEquals(message, re.getMessage());      throw re;    }    fail("Employee Id Null exception did not throw!");  }