Write unittests about pyfolio

[twiecki]

I started here: https://github.com/quantopian/quantrisk/blob/master/quantrisk/tests/test_timeseries.py

[twiecki]

Further down the line if we want to unittest plotting functions, this seems handy: https://github.com/astrofrog/pytest-mpl

[gusgordon]

@twiecki Can you review my commit here: 1b04a24? There are a couple functions (multi_factor_alpha, calc_alpha_beta) I could not figure out how to write tests for, commented out towards the bottom.

Also, just a list of functions that we don't have tests for:
out_of_sample_vs_in_sample_returns_kde
calc_multifactor
multi_factor_alpha
calc_alpha_beta
cone_rolling
gen_date_ranges_interesting
extract_interesting_date_ranges

Any of these we want tests for? Likely multi_factor_alpha and calc_alpha_beta like I mentioned above.

One this is sorted out we can close.

[twiecki]

I think we can do without these tests for the beta 👍.