@raises(ValueError)
def test_index_mismatch():
    apparent_zenith = pd.Series([30])
    apparent_azimuth = pd.Series([90,180])

    tracker_data = tracking.singleaxis(apparent_zenith, apparent_azimuth,
                                       axis_tilt=0, axis_azimuth=90,
                                       max_angle=90, backtrack=True, 
                                       gcr=7.0/2.0)
dataset/ETHPy150Open pvlib/pvlib-python/pvlib/test/test_tracking.py/test_index_mismatch/swapped operands of `/`