* WIP: start to use the PyScriptTests machinery to test the examples
* factor test_hello_world out of test_examples
* B011 forbids 'assert False' in tests because python -O remove asserts. Thank you, I knew that.
* improve test_simple_clock and remove it from test_examples
* test_altair
* test_bokeh
* rename
* kill the parametrized test_example and write individual tests for each of them
* test_kmeans it's slow, increase the timeout
* improve these xfail
* kill wait_for_load, no longer needed
* write the name of the issue
* add issue number
* add a trick which I discovered to run test interactively
* move the docstring inside the class
