def METHOD_NAME(panel_data) -> None:
    cov = HomoskedasticCovariance(
        panel_data.y,
        panel_data.x,
        panel_data.params,
        panel_data.entity_ids,
        panel_data.time_ids,
        extra_df=0,
    ).cov
    assert cov.shape == (panel_data.k, panel_data.k)
    cov = HomoskedasticCovariance(
        panel_data.y,
        panel_data.x,
        panel_data.params,
        panel_data.entity_ids,
        panel_data.time_ids,
        extra_df=0,
    ).cov
    assert cov.shape == (panel_data.k, panel_data.k)