added mock to test dependencies

tox.ini

@@ -36,6 +36,7 @@ setenv=
     COVERAGE_FILE={env:TOXINI_COVERAGE_FILE:{toxinidir}/.coverage}
 # Additional dependencies
 deps=
+    mock
     coverage
     django111: Django>=1.11,<2.0
     django20: Django>=2.0,<2.1
@@ -52,6 +53,7 @@ deps=
 #   We specify a specific version of flake8 to avoid introducing "false"
 #   regressions when new checks are introduced. The version of flake8 used may
 #   be overridden via the TOXINI_FLAKE8_VERSION environment variable.
+    mock
     flake8=={env:TOXINI_FLAKE8_VERSION:3.6.0}
 commands=
     flake8 --version
@@ -61,6 +63,7 @@ commands=
 [testenv:coverage]
 basepython=python3
 deps=
+    mock
     coverage
     django
 # Specify the default environment. Note that tox will *always* use the testsuite