CI: Add separate test environment for pytz

The separate tests with and without pytz are done to try to minimize the
possibility of implicit dependencies on pytz.

Run the second test in it's own entry in the script section of the
travis file so that it does not mask failures from other sections.

Author: pganssle

.travis.yml

@@ -158,14 +158,18 @@ before_script: |
   fi
 
 script:
+  # each script we want to run need to go in it's own section and the program you want
+  # to fail travis need to be the last thing called
   - |
     echo "Calling pytest with the following arguments: $PYTEST_ADDOPTS"
     python -mpytest
+  - tox -e pytz
   - |
     if [[ $RUN_FLAKE8 == 1 ]]; then
       flake8 --statistics && echo "Flake8 passed without any issues!"
     fi
 
+
 before_cache: |
   rm -rf $HOME/.cache/matplotlib/tex.cache
   rm -rf $HOME/.cache/matplotlib/test_cache

requirements/testing/travis_all.txt

@@ -17,3 +17,4 @@ pytest-xdist
 python-dateutil
 sphinx
 tornado
+tox

tox.ini

@@ -18,3 +18,11 @@ commands =
     pytest --pyargs matplotlib
 deps =
     pytest
+
+[testenv:pytz]
+changedir = /tmp
+commands =
+    pytest -m pytz {toxinidir}
+deps =
+    pytest
+    pytz