def METHOD_NAME(self):
    #- Create a fake sky
    self.nspec = 20
    self.wave = np.arange(4000, 4502)
    self.nwave = len(self.wave)
    self.flux = np.zeros(self.nwave)
    for i in range(0, self.nwave, 20):
        self.flux[i] = i
    self.ivar = np.ones(self.flux.shape)
    self.mask = np.zeros(self.flux.shape, dtype=np.int32)
    self.tpcorr = np.linspace(0.9, 1.1, self.nspec)
    self.add_variance = True