chore(TCs): mark SLOW tests, when in hurry, +setup.cfg

... to adopt pytest args
+ mark wheel a universal.

.travis.yml

@@ -22,6 +22,8 @@ install:
 
 script:
   - pytest -v --cov=graphkit
+  # In case you adopt -m 'not slow' in setup.cfg.
+  #- pytest -vm slow --cov=graphkit
 
 deploy:
   provider: pypi

setup.cfg

@@ -0,0 +1,10 @@
+## Python's setup.cfg for tool defaults:
+#
+[bdist_wheel]
+universal = 1
+
+
+[tool:pytest]
+# See http://doc.pytest.org/en/latest/mark.html#mark
+markers =
+    slow: marks tests as slow, select them with `-m slow` or `-m 'not slow'`

test/test_graphkit.py

@@ -578,6 +578,7 @@ def count_deletions(steps):
     assert count_deletions(steps12) != count_deletions(steps22)
 
 
+@pytest.mark.slow
 def test_parallel_execution():
     import time
 
@@ -633,6 +634,7 @@ def fn3(z, k=1):
     # make sure results are the same using either method
     assert result_sequential == result_threaded
 
+@pytest.mark.slow
 def test_multi_threading():
     import time
     import random

test/test_plot.py

@@ -52,6 +52,7 @@ def test_plotting_docstring():
         assert ext in network.Network.plot.__doc__
 
 
+@pytest.mark.slow
 def test_plot_formats(pipeline, tmp_path):
     ## Generate all formats  (not needing to save files)