Graphical test and automated test-execution

Some test are conceptualized as looking at a plot, which is hard to do automatically. Construction of the sequences before plotting could however catch a lot of bugs even without looking at the plots. Therefore, is might be useful to run all tests automatically without actually plotting.

To achieve this the plotting routine could be wrapped in a conditional skipping if a environment Variable is set accordingly.

...
with self.subTest(msg="Plotting all waveforms"):
    if os.environ.get("SKIP_GRAPHICAL", True):
         self.skipTest(reason="Graphical tests are skipped")