Use the new testing machinery for test_examples (#676)

* 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

pyscriptjs/tests/support.py

@@ -66,6 +66,15 @@ class PyScriptTest:
         # this extra print is useful when using pytest -s, else we start printing
         # in the middle of the line
         print()
+        #
+        # if you use pytest --headed you can see the browser page while
+        # playwright executes the tests. However, the page is closed very
+        # quickly as soon as the test finishes. If you want to pause the test
+        # to have time to inspect it manually, uncomment the next two
+        # lines. The lines after the 'yield' will be executed during the
+        # teardown, leaving the page open until you exit pdb.
+        ## yield
+        ## import pdb;pdb.set_trace()
 
     def init_page(self, page):
         self.page = page