Add Flask example and tests

[greyli]

This is a basic example for Flask and some universal tests for all the examples. The app generally follows the design in #1, the only difference is that I remove the age field.

After it's merged, I will start to set up the repo (tox, pre-commit hook, CI, etc.).

[jugmac00]

First, thank you so much for putting so much effort into showcasing Flask's capabilities to provide web APIs.

A couple of remarks:

• README.md is missing
• requirements.txt is missing
• it would be nice to have some curl commands for copy pasting at the top level README to play with the API

Additionally, I have left some inline comments.

Btw, what is the reason to not support PUT?

Could you please explain the indirect=True parameter for parametrize? I had a look at pytests docs, but I am still puzzled.
Disclaimer, I don't work a lot with REST API.

I used curl to query the API, and looks good from my side!

[greyli]

Thanks for the review, I just added the missing README.md and requirements.txt/in files, and moved error messages and category list to separate variables.

it would be nice to have some curl commands for copy pasting at the top level README to play with the API

Sure, I will add it later.

what is the reason to not support PUT?

The PUT for updating a resource will be duplicate most of the update_pet view, so I think only support PATCH is enough for an example application.

Could you please explain the indirect=True parameter for parameterized?

It will pass the items in the example list to the client fixture (via request.param), so we can iterate all the example applications for each test.

[jugmac00]

Some more minor comments 👍