Create documentation for testing server endpoints.

Currently the sanic.utils functionality is undocumented. This provides
information on the interface as well as a complete example of testing
a server endpoint.

README.md

@@ -59,6 +59,7 @@ if __name__ == "__main__":
  * [Class Based Views](docs/class_based_views.md)
  * [Cookies](docs/cookies.md)
  * [Static Files](docs/static_files.md)
+ * [Testing](docs/testing.md)
  * [Deploying](docs/deploying.md)
  * [Contributing](docs/contributing.md)
  * [License](LICENSE)

docs/testing.md

@@ -0,0 +1,51 @@
+# Testing
+
+Sanic endpoints can be tested locally using the `sanic.utils` module, which
+depends on the additional [aiohttp](https://aiohttp.readthedocs.io/en/stable/)
+library. The `sanic_endpoint_test` function runs a local server, issues a
+configurable request to an endpoint, and returns the result. It takes the
+following arguments:
+
+- `app` An instance of a Sanic app.
+- `method` *(default `'get'`)* A string representing the HTTP method to use.
+- `uri` *(default `'/'`)* A string representing the endpoint to test.
+- `gather_request` *(default `True`)* A boolean which determines whether the
+  original request will be returned by the function. If set to `True`, the
+  return value is a tuple of `(request, response)`, if `False` only the
+  response is returned.
+- `loop` *(default `None`)* The event loop to use.
+- `debug` *(default `False`)* A boolean which determines whether to run the
+  server in debug mode.
+
+The function further takes the `*request_args` and `**request_kwargs`, which
+are passed directly to the aiohttp ClientSession request. For example, to
+supply data with a GET request, `method` would be `get` and the keyword
+argument `params={'value', 'key'}` would be supplied. More information about
+the available arguments to aiohttp can be found
+[in the documentation for ClientSession](https://aiohttp.readthedocs.io/en/stable/client_reference.html#client-session).
+
+Below is a complete example of an endpoint test,
+using [pytest](http://doc.pytest.org/en/latest/). The test checks that the
+`/challenge` endpoint responds to a GET request with a supplied challenge
+string.
+
+```python
+import pytest
+import aiohttp
+from sanic.utils import sanic_endpoint_test
+
+# Import the Sanic app, usually created with Sanic(__name__)
+from external_server import app
+
+def test_endpoint_challenge():
+    # Create the challenge data
+    request_data = {'challenge': 'dummy_challenge'}
+
+    # Send the request to the endpoint, using the default `get` method
+    request, response = sanic_endpoint_test(app,
+                                            uri='/challenge',
+                                            params=request_data)
+
+    # Assert that the server responds with the challenge string
+    assert response.text == request_data['challenge']
+```