def test_empty_histogram() :
h = Histogram(axis=Axis(100,-50, 50))
assert h.entries() == 0.
assert h.sigma() == 0
assert h.mean() == 0
assert h.overflow() == 0
assert h.underflow() ==0
def test_sigma() :
h0 = Histogram(axis=Axis(100, -50., 50.))
h0.fill([5.5,-5.5,100.5,-100.5])
assert h0.sigma() == 5.5