NumPy version 1.13.1

np.testing.assert_array_equal(np.array([]), np.nan) doesn't raise an AssertionError although according to the docs it definitely should - if not for their different values then at least for their different shapes (the nan produced by np.array([]).mean() has a shape).

If this is desired behaviour for a reason I'm overlooking, maybe we should clarify this in the docs. If it's unexpected behaviour this is quite dangerous.