def test_plot_bad_index():
import matplotlib.pyplot as plt
idx = sorted(
[f"{a}{b}{c}" for a, b, c, in product(*([ascii_lowercase] * 3))])
sp500_copy = SP500.copy()
sp500_copy.index = idx[:sp500_copy.shape[0]]
res = ConstantMean(sp500_copy).fit(disp=False)
fig = res.plot()
assert isinstance(fig, plt.Figure)
