How can I fake request.POST and GET params for unit testing in Flask?

Did you read Flask docs about testing?

You can use following:

self.app.post('/path-to-request', data=dict(var1='data1', var2='data2', ...))
self.app.get('/path-to-request', query_string=dict(arg1='data1', arg2='data2', ...))

Current development version of Flask also includes support for testing JSON APIs:

from flask import request, jsonify

@app.route('/jsonapi')
def auth():
    json_data = request.get_json()
    attribute = json_data['attr']
    return jsonify(resp=generate_response(attribute))

with app.test_client() as c:
    rv = c.post('/jsonapi', json={
        'attr': 'value', 'other': 'data'
    })
    json_data = rv.get_json()
    assert generate_response(email, json_data['resp'])

POST:

self.app.post('/endpoint', data=params)

GET:

self.app.get('/endpoint', query_string=params)