test_one_thing.java

public class ThingTester {
  
  private ThingDoer doer = new ThingDoer();
    
  @Test
  public void testAllTheThings() {
    assertThat(doer.doTheThing(), is("theThing"));
    assertThat(doer.doTheOtherThing(), is("theOtherThing"));
    assertThat(doer.doTheThirdThing(), is(false));
    // Repeat for 39 more assertions...
  }

  @Test
  public void testOneThing() {
    assertThat(doer.doTheThing(), is("theThing"));
  }
}