Set up test files and added model save test.
Added test to check that proceess_transaction only runs once.
Added valid environment test.
Added tests for environment settings.
Trivial comment change.
Merge remote-tracking branch 'upstream/master' into add-tests
Refactored save tests and added valid environment and has card/customer token tests.
Added test to check for valid JSON response.
Fixed assert orders.
Oops, assertRaises requires error class first.
Added error message tests.
Added successful transaction test.
Added Mock requirement to readme.
Added customer token save test.
Added create card token environment tests
Added create token valid environment tests.
Added tests for create token success and errors.
Added template tags tests.
Merge pull request #1 from huwshimi/add-tests

Add unit tests for models and template tags. Thanks @huwshimi