fix: tox: modified the tox test process to work around a backward-com…

…patibility-breaking change introduced by coverage.py Version 4.2b1 --- 2016-07-04.

Details:
... The "coverage combine" command now will ignore an existing .coverage data file, rather than appending to it as it used to do. ...
... There's also a new "--append" option on "coverage combine", so you can get the old behavior ...
see: http://nedbatchelder.com/blog/201607/coveragepy_42.html
see: https://bitbucket.org/ned/coveragepy/src/tip/CHANGES.rst?fileviewer=file-view-default

tox.ini

@@ -91,7 +91,14 @@ deps =
     coveralls
 skip_install = true
 commands =
-    coverage combine
+    ; NOTE: FIX: fix for a backward incompatibility introduced by coverage.py Version 4.2b1 --- 2016-07-04
+    ; ... The "coverage combine" command now will ignore an existing .coverage data file,
+    ;     rather than appending to it as it used to do. ...
+    ; ... There's also a new "--append" option on "coverage combine", so you can get the old behavior ...
+    ; see: http://nedbatchelder.com/blog/201607/coveragepy_42.html
+    ; see: https://bitbucket.org/ned/coveragepy/src/tip/CHANGES.rst?fileviewer=file-view-default
+    ; coverage combine
+    coverage combine --append
     coverage report
     coveralls []
 
@@ -100,8 +107,8 @@ deps =
     codecov
 skip_install = true
 commands =
-    coverage combine
-    coverage report
+    ; coverage combine --append
+    ; coverage report
     coverage xml --ignore-errors
     codecov []
 
@@ -110,7 +117,7 @@ commands =
 deps = coverage
 skip_install = true
 commands =
-    coverage combine
+    coverage combine --append
     coverage report
     coverage html