Added testing docs

Author: syrusakbary

docs/index.rst

@@ -10,6 +10,7 @@ Contents:
    types/index
    execution/index
    relay/index
+   testing/index
 
 Integrations
 -----

docs/testing/index.rst

@@ -0,0 +1,90 @@
+===================
+Testing in Graphene
+===================
+
+
+Automated testing is an extremely useful bug-killing tool for the modern developer. You can use a collection of tests – a test suite – to solve, or avoid, a number of problems:
+
+- When you’re writing new code, you can use tests to validate your code works as expected.
+- When you’re refactoring or modifying old code, you can use tests to ensure your changes haven’t affected your application’s behavior unexpectedly.
+
+Testing a GraphQL application is a complex task, because a GraphQL application is made of several layers of logic – schema definition, schema validation, permissions and field resolution.
+
+With Graphene test-execution framework and assorted utilities, you can simulate GraphQL requests, execute mutations, inspect your application’s output and generally verify your code is doing what it should be doing.
+
+
+Testing tools
+-------------
+
+Graphene provides a small set of tools that come in handy when writing tests.
+
+
+Test Client
+~~~~~~~~~~~
+
+The test client is a Python class that acts as a dummy GraphQL client, allowing you to test your views and interact with your Graphene-powered application programmatically.
+
+Some of the things you can do with the test client are:
+
+- Simulate Queries and Mutations and observe the response.
+- Test that a given query request is rendered by a given Django template, with a template context that contains certain values.
+
+
+Overview and a quick example
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To use the test client, instantiate ``graphene.test.Client`` and retrieve GraphQL responses:
+
+
+.. code:: python
+
+    from graphene.test import Client
+
+    def test_hey():
+        client = Client(my_schema)
+        executed = client.execute('''{ hey }''')
+        assert executed == {
+            'data': {
+                'hey': 'hello!'
+            }
+        }
+
+
+Snapshot testing
+~~~~~~~~~~~~~~~~
+
+As our APIs evolve, we need to know when our changes introduce any breaking changes that might break
+some of the clients of our GraphQL app.
+
+However, writing tests and replicate the same response we expect from our GraphQL application can be
+tedious and repetitive task, and sometimes it's easier to skip this process.
+
+Because of that, we recommend the usage of `SnapshotTest <https://github.com/syrusakbary/snapshottest/>`_.
+
+SnapshotTest let us write all this tests in a breeze, as creates automatically the ``snapshots`` for us
+the first time the test is executed.
+
+
+Here is a simple example on how our tests will look if we use ``pytest``:
+
+.. code:: python
+
+    def test_hey(snapshot):
+        client = Client(my_schema)
+        # This will create a snapshot dir and a snapshot file
+        # the first time the test is executed, with the response
+        # of the execution.
+        snapshot.assert_match(client.execute('''{ hey }'''))
+
+
+If we are using ``unittest``:
+
+.. code:: python
+    
+    from snapshottest import TestCase
+
+    class APITestCase(TestCase):
+        def test_api_me(self):
+            """Testing the API for /me"""
+            client = Client(my_schema)
+            self.assertMatchSnapshot(client.execute('''{ hey }'''))