Add tests

[treyhunner]

I think all code should have tests.

The tests shouldn't depend on the Authorize.NET servers so [mock][] should probably be used to mock calls to request.post and other network calls as needed.

I may turn this into a pull request if I decide to start writing some tests.

Goals of this PR:

• Add basic test suite allowing python setup.py test to work
• Add a few example tests
• Add tox file for supported Python/Django versions
• Add Travis and Coveralls support

[zen4ever]

Yes, either mock or httmock (from #22), whatever makes more sense.

[treyhunner]

I converted this to a pull request and added a checklist to the description.

Which Python/Django versions should be tested? The current tox file I've added tests Python 2.6 and 2.7 and Django 1.4, 1.5, and trunk.

[zen4ever]

Yes. Supporting those versions seems reasonable to me. We need Python
2.6 since it goes by default on current version of Amazon Linux. And
hopefully supporting two versions of Django would be enough.

[treyhunner]

@zen4ever can you enable the repository on Travis CI? Travis adds a post-receive hook on Github which requires admin access to add.

[zen4ever]

@treyhunner should be enabled now

[coveralls]

Changes Unknown when pulling 9f11aa6 on tests into * on master*.

[treyhunner]

I went with httmock because it's simple.

I added a couple example tests including a test for one of the add_profile success cases.

I added Travis and Coveralls badges to the README file. I can remove that commit if you don't like showing those in the README.

I disabled the coveralls comments on pull requests (they happen on every push which can get annoying).

I think this is ready to be merged now. There are very few tests currently, but some tests are better than none.

[zen4ever]

Looks good. Feel free to merge it. I will try to add some more tests later.