title: Unit tests with nested objects in the request using flask
body: <p>How can one unit test a REST API endpoint written in flask that accepts a nested dictionary object for the request body?</p>
  
  <p>Here is an example using flask and webargs for input validation,</p>
  
  <pre><code>from flask import Flask
  from webargs import fields
  from webargs.flaskparser import use_args
  
  app = Flask(__name__)
  
  hello_args = { 
      'a': fields.Nested({'name' : fields.Str()})
  }
  
  @app.route('/', methods=['POST'])
  @use_args(hello_args)
  def index(args):
      return 'Hello ' + str(args)
  
  
  def test_app():
      app.config['TESTING'] = True
      test_app = app.test_client(use_cookies=False)
      test_app.post(data={"a": {"name": "Alice"}})
  
  
  if __name__ == '__main__':
      app.run()
  </code></pre>
  
  <p>which works correctly when using this enpoint directly,</p>
  
  <pre><code>% curl -H "Content-Type: application/json" -X POST \
         -d '{"a":{"name": "Alice"}}' http://localhost:5000  
  
  Hello {'a': {'name': 'Alice'}}%
  </code></pre>
  
  <p>however raises an exception in <code>werkzeug.test.EnvironBuilder</code> when it is called inside unit-tests,</p>
  
  <pre><code>nosetests /tmp/test.py                                                      
  E
  ======================================================================
  ERROR: test.test_app
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "/usr/lib64/python3.4/site-packages/nose/case.py", line 198, in runTest
      self.test(*self.arg)
    File "/tmp/test.py", line 26, in test_app
      test_app.post(data={"a": {"name": "Alice"}})
    File "/home/rth/.local/lib64/python3.4/site-packages/werkzeug/test.py", line 788, in post
      return self.open(*args, **kw)
    File "/home/rth/.local/lib64/python3.4/site-packages/flask/testing.py", line 103, in open
      builder = make_test_environ_builder(self.application, *args, **kwargs)
    File "/home/rth/.local/lib64/python3.4/site-packages/flask/testing.py", line 34, in make_test_environ_builder
      return EnvironBuilder(path, base_url, *args, **kwargs)
    File "/home/rth/.local/lib64/python3.4/site-packages/werkzeug/test.py", line 338, in __init__
      self._add_file_from_data(key, value)
    File "/home/rth/.local/lib64/python3.4/site-packages/werkzeug/test.py", line 355, in _add_file_from_data
      self.files.add_file(key, **value)
  TypeError: add_file() got multiple values for argument 'name'
  
  ----------------------------------------------------------------------
  Ran 1 test in 0.011s
  
  FAILED (errors=1)
  </code></pre>
  
  <p>this uses Python 3.5, flask 0.12 and webargs 1.5.2.</p>
  
  <p>Also submitted an issue at <a href="https://github.com/pallets/flask/issues/2176" rel="nofollow noreferrer">https://github.com/pallets/flask/issues/2176</a></p>