This works for me. Can you add a test? https://matplotlib.org/devel/testing.html I guess this needs an image test, but can you remember to set style='mpl20', remove_text=True in the @image_comparparison parameters?

I guess a test could look like this, just checking if the path has indeed been updated.

def test_set_drawstyle():
    import numpy as np
    import matplotlib.pyplot as plt
    x = np.linspace(0, 2*np.pi, 10)
    y = np.sin(x)

    fig, ax = plt.subplots() 
    line, = ax.plot(x, y)
    line.set_drawstyle("steps-pre") 
    assert len(line.get_path().vertices) == 2*len(x)-1
    line.set_drawstyle("default")
    assert len(line.get_path().vertices) == len(x)

Where exactly would I add this test? I can't find a matplotlib/test directory on my fork.

lib/matplotlib/tests. Probably in test_lines.py?

Ok, found it. Thanks.

This isn't really urgent for 2.2, but is small enough that it should be quick to review

was going to abstain given that I basiclaly posted the patch, but I guess @ImportanceOfBeingErnest also likes it so...