[BUG] [python-flask] server doesn't work, crashes on tests

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

I generated code from a spec, and tried to run the tests.

The tests fail out of the box because they're missing required fields. (Which is a separate issue.)
When I add that, I get another test failure, because nothing is passed to the controller function.

openapi-generator version

$ docker run --rm     -v $PWD:/local     openapitools/openapi-generator-cli --version                        
openapi-generator-cli 5.0.0-SNAPSHOT
  commit : 59029d2
  built  : 2020-07-29T03:01:05Z
  source : https://github.com/openapitools/openapi-generator
  docs   : https://openapi-generator.tech/

OpenAPI declaration file content or url

openapi: 3.0.1
info:
  title: MWE
  description: example of bug in generator
  version: 1.0.0
servers:
- url: http://example.com/api
paths:
  /go:
    post:
      summary: POST request
      operationId: post_thing
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/post-request'
        required: true
      responses:
        201:
          description: pending
          content: {}
components:
  schemas:
    post-request:
      required:
      - user
      type: object
      properties:
        user:
          type: string
          description: The user who initiated the request
          example: test user

Command line used for generation

docker run --rm \
    -v $PWD:/local \
    openapitools/openapi-generator-cli \
    generate \
    -i /local/mwe.yaml \
    -g python-flask \
    -o /local/out-mwe \
    --package-name example

Steps to reproduce

• generate with command and spec from above
• modify test_default_controller.py, function test_post_thing, variable post_request to be {'user': 'some user'}
• from the folder that is a parent of the example folder, run python3 -m unittest

Expected behavior

Tests pass

Actual behavior

$ python3 -m unittest
[2020-07-29 23:04:11,960] ERROR in app: Exception on /api/go [POST]
Traceback (most recent call last):
  File "/home/ec2-user/.local/lib/python3.6/site-packages/flask/app.py", line 2446, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/ec2-user/.local/lib/python3.6/site-packages/flask/app.py", line 1951, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/ec2-user/.local/lib/python3.6/site-packages/flask/app.py", line 1820, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/home/ec2-user/.local/lib/python3.6/site-packages/flask/_compat.py", line 39, in reraise
    raise value
  File "/home/ec2-user/.local/lib/python3.6/site-packages/flask/app.py", line 1949, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/ec2-user/.local/lib/python3.6/site-packages/flask/app.py", line 1935, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/ec2-user/.local/lib/python3.6/site-packages/connexion/decorators/decorator.py", line 48, in wrapper
    response = function(request)
  File "/home/ec2-user/.local/lib/python3.6/site-packages/connexion/decorators/uri_parsing.py", line 172, in wrapper
    response = function(request)
  File "/home/ec2-user/.local/lib/python3.6/site-packages/connexion/decorators/validation.py", line 184, in wrapper
    response = function(request)
  File "/home/ec2-user/.local/lib/python3.6/site-packages/connexion/decorators/parameter.py", line 121, in wrapper
    return function(**kwargs)
TypeError: post_thing() missing 1 required positional argument: 'post_request'
F
======================================================================
FAIL: test_post_thing (example.test.test_default_controller.TestDefaultController)
Test case for post_thing
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/ec2-user/environment/dispatch_swagger/out-mwe/example/test/test_default_controller.py", line 34, in test_post_thing
    'Response body is : ' + response.data.decode('utf-8'))
  File "/home/ec2-user/.local/lib/python3.6/site-packages/flask_testing/utils.py", line 336, in assert200
    self.assertStatus(response, 200, message)
  File "/home/ec2-user/.local/lib/python3.6/site-packages/flask_testing/utils.py", line 324, in assertStatus
    self.assertEqual(response.status_code, status_code, message)
AssertionError: 500 != 200 : Response body is : {
  "detail": "The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.",
  "status": 500,
  "title": "Internal Server Error",
  "type": "about:blank"
}


----------------------------------------------------------------------
Ran 1 test in 0.026s

FAILED (failures=1)

Related issues/PRs

Suggest a fix

No idea what's gone wrong here.

Reproduce the issue with the supplied OpenAPI declaration and generation command, then inspect the generated test/test_default_controller.py and the post_thing controller path. Run python3 -m unittest from the parent of the example folder and trace why post_request is not passed to post_thing. Done means the generated test receives the request body and passes with a 200 response.