Add json argument to test.Client.post()

[jwg4]

Hi there. I wondered if it would be useful to have an argument json for the method test.Client.post(). The idea would be that you can pass in a request body in the form of a data structure which gets serialized to JSON.
You would not be able to set both data and json, it would simply be a convenience rather than serialize to JSON and then pass in as data.
This argument is present in requests.post() and one reason it might be nice to have it is that makes it possible to keep testing with the Werkzeug client and live testing/monitoring against a production server using Requests closer together.
I am happy to submit a PR for this, but I wanted to check first in case it is seen as bloaty or not a good idea for some other reason. Thanks!

[DoWhileGeek]

I heavily agree with this idea. I was actually skimming issues to see if theres any talk about a json attribute or method planned for the Response object, I'm probably going to end up creating an issue for this like you did.

[jeffwidman]

Related: pallets/flask#1416

[coilysiren]

To expand on the spec above, currently I do

    response = app.post(
        '/snippets',
        data=json.dumps({'text': 'example'}),
        content_type='application/json',
    )

whereas I would like to do

    response = app.post(
        '/snippets',
        json={'text': 'example'},
    )

[coilysiren]

Looks like #950 was on the way to getting this done, just needs someone with capacity to finish it!

[coilysiren]

( last comment I promise !!! )

Looks like this is in already! http://flask.pocoo.org/docs/1.0/testing/#testing-json-apis ✨