def test_cross_treshold_empty():
y = pd.Series(data=[np.nan, 1, 3, 1], index=[2002, 2005, 2007, 2013])
obs = cross_threshold(y, 4)
assert obs == []
def test_cross_treshold_from_above():
y = pd.Series(data=[np.nan, 1, 3, 1], index=[2002, 2005, 2007, 2013])
obs = cross_threshold(y, 2, direction="from above")
assert obs == [2011]
def test_cross_treshold_from_below():
y = pd.Series(data=[np.nan, 1, 3, 1], index=[2002, 2005, 2007, 2013])
obs = cross_threshold(y, 2, direction='from below')
assert obs == [2007]