✨ Add testing docs and tests (#151)

* ✏️ Fix typo in security intro

* ✨ Add testing docs and tests

* 🐛 Debug Travis coverage

* 🐛 Debug Travis coverage, report XML

* 💚 Make Travis/Flit use same code install

* ⏪ Revert Travis/Codecov debugging changes

docs/tutorial/security/intro.md

@@ -20,7 +20,7 @@ It is quite an extensive specification and covers several complex use cases.
 
 It includes ways to authenticate using a "third party".
 
-That's what all the system with "login with Facebook, Google, Twitter, GitHub" use underneath.
+That's what all the systems with "login with Facebook, Google, Twitter, GitHub" use underneath.
 
 ### OAuth 1
 

docs/tutorial/testing.md

@@ -0,0 +1,69 @@
+Thanks to <a href="https://www.starlette.io/testclient/" target="_blank">Starlette's TestClient</a>, testing **FastAPI** applications is easy and enjoyable.
+
+It is based on <a href="http://docs.python-requests.org" target="_blank">Requests</a>, so it's very familiar and intuitive.
+
+With it, you can use <a href="https://docs.pytest.org/" target="_blank">pytest</a> directly with **FastAPI**.
+
+## Using `TestClient`
+
+Import `TestClient` from `starlette.testclient`.
+
+Create a `TestClient` passing to it your **FastAPI**.
+
+Create functions with a name that starts with `test_` (this is standard `pytest` conventions).
+
+Use the `TestClient` object the same way as you do with `requests`.
+
+Write simple `assert` statements with the standard Python expressions that you need to check (again, standard `pytest`).
+
+```Python hl_lines="2 12 15 16 17 18"
+{!./src/app_testing/tutorial001.py!}
+```
+
+!!! tip
+    Notice that the testing functions are normal `def`, not `async def`. 
+    
+    And the calls to the client are also normal calls, not using `await`.
+
+    This allows you to use `pytest` directly without complications.
+
+
+## Separating tests
+
+In a real application, you probably would have your tests in a different file.
+
+And your **FastAPI** application might also be composed of several files/modules, etc.
+
+### **FastAPI** app file
+
+Let's say you have a file `main.py` with your **FastAPI** app:
+
+```Python
+{!./src/app_testing/main.py!}
+```
+
+### Testing file
+
+Then you could have a file `test_main.py` with your tests, and import your `app` from the `main` module (`main.py`):
+
+```Python
+{!./src/app_testing/test_main.py!}
+```
+
+## Testing WebSockets
+
+You can use the same `TestClient` to test WebSockets.
+
+For this, you use the `TestClient` in a `with` statement, connecting to the WebSocket:
+
+```Python hl_lines="27 28 29 30 31"
+{!./src/app_testing/tutorial002.py!}
+```
+
+## Testing Events, `startup` and `shutdown`
+
+When you need your event handlers (`startup` and `shutdown`) to run in your tests, you can use the `TestClient` with a `with` statement:
+
+```Python hl_lines="9 10 11 12 20 21 22 23 24"
+{!./src/app_testing/tutorial003.py!}
+```