@Test
 public void should_return_this() {
   ConcreteCollectionAssert returned = assertions.containsNull();
   assertSame(assertions, returned);
 }
 @Test
 public void should_verify_that_actual_contains_null() {
   assertions.containsNull();
   verify(collections).assertContainsNull(assertions.info, assertions.actual);
 }
 @Test
 public void should_return_this() {
   ConcreteCollectionAssert returned = assertions.isNotEmpty();
   assertSame(assertions, returned);
 }
 @Before
 public void setUp() {
   collections = mock(Collections.class);
   assertions = new ConcreteCollectionAssert(emptyList());
   assertions.collections = collections;
 }
 @Test
 public void should_verify_that_actual_is_not_empty() {
   assertions.isNotEmpty();
   verify(collections).assertNotEmpty(assertions.info, assertions.actual);
 }