Comparison with None

[chillenzer]

The idiomatic way of comparing with None is x is (not) None as opposed to x == None. I could see a weak argument about the symmetry in the 4 assertion statements in the edge and corner cases section to leave it that way but I would suggest using the idiomatic form.

[edbennett]

Agree, use is None. (Also adding extra spaces to line up equals signs isn't PEP8.)

[chillenzer]

The first change in my editor will have black applied on saving, so consider it fixed. =)