@anntzer one reason I did not implement the complete empty plot test mentioned in the previous PR was that that test would pass even if there is nothing being done while plotting?

Yes, but it's extremely unlikely that we'd ever introduce a bug such that ax.spines[:].set_visible(False); ax.set(xticks=[], yticks=[]) would actually disable all drawing.
If you want to feel extra safe I would still do a check_figures_equal where the reference figure has all axes manually made transparent with set_facecolor("none") calls.

Ah okay. Yeah, I'll do that then. Thanks.

I had a quick question. Since this is related to a savefig parameter, I'll need to pass that to the savefig function inside the decorator. From what I can see, that's not possible right now with check_figures_equal?

@anntzer any suggestions on this?

Something like

@mpl.rc_context({"savefig.transparent": True})
@check_figures_equal(extensions=["png"])
def test_savefig_transparent(fig_test, fig_ref):
    # create two transparent subfigures with corresponding transparent inset
    # axes. the entire background of the image should be transparent.
    gs1 = fig_test.add_gridspec(3, 3, left=0.05, wspace=0.05)
    f1 = fig_test.add_subfigure(gs1[:, :])
    f2 = f1.add_subfigure(gs1[0, 0])

    ax12 = f2.add_subplot(gs1[:, :])

    ax1 = f1.add_subplot(gs1[:-1, :])
    iax1 = ax1.inset_axes([.1, .2, .3, .4])
    iax2 = iax1.inset_axes([.1, .2, .3, .4])

    ax2 = fig_test.add_subplot(gs1[-1, :-1])
    ax3 = fig_test.add_subplot(gs1[-1, -1])

    for ax in [ax12, ax1, iax1, iax2, ax2, ax3]:
        ax.set(xticks=[], yticks=[])
        ax.spines[:].set_visible(False)

    # and draw nothing on fig_ref.

?

Did not know about mpl.rc_context. This should work, thanks!