The `actual` and `expected` properties on an instance of
`AssertionError` is now a getter to prevent inspecting these when
inspecting the error. These values will be visible in the error
message and showing them otherwise would decrease the readability
of the error.

One test did not cause an assertion. By changing the test to use
`assert.throws()` all tests have to throw, otherwise the test will
fail.

Co-Authored-By: BridgeAR <ruben@bridgewater.de>