Install test requirements explicitly

.travis.yml

@@ -40,7 +40,7 @@ install:
 
     for pv in "2.7" "3.4" "3.5"; do
         source ~/virtualenv/python${pv}/bin/activate
-        for p in '-r requirements.txt' 'behave codacy-coverage coverage coveralls'; do
+        for p in '-r requirements.txt' 'behave codacy-coverage coverage coveralls flake8 mock pytest-cov pytest'; do
             pip install $p
         done
     done