@Test void getOnlyElementWithEmptyCollection() { PreconditionViolationException exception = expectThrows( PreconditionViolationException.class, () -> { CollectionUtils.getOnlyElement(emptySet()); }); assertEquals("collection must contain exactly one element: []", exception.getMessage()); }
@Test void getOnlyElementWithMultiElementCollection() { PreconditionViolationException exception = expectThrows( PreconditionViolationException.class, () -> { CollectionUtils.getOnlyElement(asList("foo", "bar")); }); assertEquals("collection must contain exactly one element: [foo, bar]", exception.getMessage()); }
@Test void getOnlyElementWithNullCollection() { PreconditionViolationException exception = expectThrows( PreconditionViolationException.class, () -> { CollectionUtils.getOnlyElement(null); }); assertEquals("collection must not be null", exception.getMessage()); }