Display an optional message on test failure

[emaadmanzoor]

Here is a PR on adding an optional message to display on test failure. All the project's tests continue to pass after this change.

Let me know if there's anything additional required (documentation, tests) before this can be merged.

[jarus]

This is a nice change. Thanks.
Maybe you could add a default message like "HTTP Status 200 expected but got 404". Can you please add a test to make sure that the defined message is included inside of the assertion.

[emaadmanzoor]

Yes this message will be useful. I'll send in an updated PR with this and the test soon.

[jarus]

Perfect with this addition. I can merge them and publish a new release.

[emaadmanzoor]

I added a default assertion failure message, and two test cases to verify the default and a custom message.

[emaadmanzoor]

The strange expected_message in e.args[0] check is for Python 3.x, where e.message has been deprecated and replaced with tuple e.args.

[jarus]

Looks very well. Thank you.