def test_drop_obs_column():
    adata = ad.AnnData(np.array(X_list), obs=obs_dict, dtype="int32")

    subset = adata[:2]
    assert subset.is_view
    # returns a copy of obs
    assert subset.obs.drop(columns=["oanno1"]).columns.tolist() == ["oanno2", "oanno3"]
    assert subset.is_view
    # would modify obs, so it should actualize subset and not modify adata
    subset.obs.drop(columns=["oanno1"], inplace=True)
    assert not subset.is_view
    assert subset.obs.columns.tolist() == ["oanno2", "oanno3"]

    assert adata.obs.columns.tolist() == ["oanno1", "oanno2", "oanno3"]
def forcedens(title, pos, fdens, ax=0):
    """plot force densities"""
    if ax == 0:
        ax = plt.gca()
    ax.set_title(title)
    ax.grid(True)

    ax.plot(pos, [1e-3*ft for ft in fdens[0]], label='F tang')
    ax.plot(pos, [1e-3*fn for fn in fdens[1]], label='F norm')
    ax.legend()
    ax.set_xlabel('Pos / deg')
    ax.set_ylabel('Force Density / kN/m²')