Add basic testing documentation

docs/docs/guides/testing.md

@@ -0,0 +1,43 @@
+# Testing
+
+**Django Ninja** provides a test client to make it easy to test your API.
+
+To test the following API:
+```python
+from ninja import NinjaAPI, Schema
+
+api = NinjaAPI()
+router = Router()
+
+class HelloResponse(Schema):
+    msg: str
+
+@router.get("/hello", response=HelloResponse)
+def hello(request):
+    return {"msg": "Hello World"}
+
+api.add_router("", router)
+```
+
+You can use the Django test class:
+```python
+from django.test import TestCase
+from ninja.testing import TestClient
+
+class HelloTest(TestCase):
+    def test_hello(self):
+        client = NinjaTestClient(router)
+        response = client.get("/hello")
+
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.json(), {"msg": "Hello World"})
+```
+
+Arbitrary attributes can be added to the request object by passing keyword arguments to the client request methods:
+```python
+class HelloTest(TestCase):
+    def test_hello(self):
+        client = NinjaTestClient(router)
+        # request.company_id will now be set within the view
+        response = client.get("/hello", company_id=1)
+```

docs/mkdocs.yml

@@ -53,6 +53,7 @@ nav:
           - guides/response/response-renderers.md
       - Splitting your API with Routers: guides/routers.md
       - guides/authentication.md
+      - guides/testing.md
       - guides/api-docs.md
       - guides/errors.md
       - guides/urls.md