Transforms - ATR

Hi.

I use ATR so frequently to size positions and set stops, limits, etc., that I thought it would be useful to have it as a simple transform, basically a property of the security.  The history doesn't matter, only the current value at the current point in time. 

For example, 

stop_price = data[stock].price - 2 * data[stock].atr(20)

is much cleaner than:

# Set up the ATR indicator.
atr_data = ta.ATR(timeperiod=20)
=======

def handle_data(context, data):  
	...
	stop_price = data[stock].price - 2 * atr_data(data)[stock]

I had a go at the simple transform, but I'll need some guidance putting together the test.  Namely how do I set up my test data history of high, low and close prices to use for my assert calculations?

Thanks.