Add documentation on how to test requirements (home-assistant#811)

technicalpickles · balloob · commit 65f882c3387a · 2016-08-21T10:59:04.000-07:00
It's possible to test different requirement versions in development by using `pip install` to the Home Assistant's config directory's dep,
and then `hass --skip-pip`
diff --git a/source/developers/component_deps_and_reqs.markdown b/source/developers/component_deps_and_reqs.markdown
@@ -11,16 +11,33 @@ footer: true
 
 Home Assistant allows components and platforms to specify their dependencies and requirements using the variables `DEPENDENCIES` and `REQUIREMENTS`. Both are lists that contain strings.
 
+## Dependencies
+
 Dependencies are other Home Assistant components that should be setup before the platform is loaded. An example is the MQTT sensor component, which requires an active connection to an MQTT broker. If Home Assistant is unable to load and setup the MQTT component, it will not setup the MQTT sensor component.
 
 ```python
 DEPENDENCIES = ['mqtt']
 ```
 
-Requirements are Python libraries that you would normally install using `pip`. If Home Assistant is unable to install the requirements or verify it is installed, the component will fail to load.
+## Requirements
+
+Requirements are Python libraries that you would normally install using `pip` for your component. Home Assistant will try to install the requirements into the `deps` subdirectory of the Home Assistant configuration directory (`.home-assistant` by default) or verify it is already installed at startup. If that fails, the component will fail to load.
 
 Requirements is a list of strings. Each entry is a pip compatible string. For example, the media player Cast platform depends on the Python package PyChromecast v0.6.12:
 
 ```python
 REQUIREMENTS = ['pychromecast==0.6.12']
 ```
+
+During development of a component, it can be useful to test against different versions of a requirement. This can be done in two steps, using pychromecast as an example:
+
+* `pip install pychromecast==0.6.13 --target ~/.homeassistant/deps`
+* `hass --skip-pip`
+
+This will use the specified version, and prevent Home Assistant from trying to override it with what is currently in `REQUIREMENTS`.
+
+If you need to make changes to a requirement to support your component, it's also possible to pip install from a checkout of the requirement.
+
+* `git clone https://github.com/balloob/pychromecast.git`
+* `pip install ./pychromecast`
+* `hass --skip-pip`
