@SuppressWarnings("ConstantConditions")
@Test public void testSingleSharedElement() {

	// Arrange:
	final TestTransition transition = new TestTransition();
	final View firstElement = new View(context);
	// Act + Assert:
	transition.sharedElement(firstElement, "first_element");
	assertThat(transition.singleSharedElement(), is(notNullValue()));
	assertThat(transition.singleSharedElement().first, is(firstElement));
	assertThat(transition.singleSharedElement().second, is("first_element"));
	final View secondElement = new View(context);
	transition.sharedElement(secondElement, "second_element");
	assertThat(transition.singleSharedElement(), is(notNullValue()));
	assertThat(transition.singleSharedElement().first, is(firstElement));
	assertThat(transition.singleSharedElement().second, is("first_element"));
}