Update showcase tests to assert conditions outside of the context manager.

[ohmayr]

The context manager exits immediately as soon as an exception is raised i.e. any following assert statements or code within the with context are not executed. For example, the following test case will pass (even with assert 2 == 3):

def test_dummy():
  with pytest.raises(ValueError) as exc:
      raise ValueError("test")
      assert 2 == 3
      exc.value == "test"  

Therefore, showcase tests need to be updated and the assert statements need to be moved out of the with context to be executed properly. This also exposes a gap in our tests where some of them are incorrectly passing (since the assertion does not occur).