Change tests comparing floats

[adam-coogan]

According to these docs, the assertAlmostEqual(a, b) function, which essentially all of our tests use, checks round(a-b, 7) == 0. This is the wrong thing to do since we want relative errors. For example,

round(1e-20 - 5e-21, 5) == 0
>>> True

We should instead switch over to something like numpy.testing.assert_allclose(), which looks at relative errors.