The testtest_image.test_image_cursor_formatting() is intended to test mouseover formatting of masked image data.
see issue#15103 and resolution in PR#15140 .

deftest_image_cursor_formatting():fig,ax=plt.subplots()im=ax.imshow(np.zeros((4,4)))data=np.ma.masked_array([0],mask=[True])assertim.format_cursor_data(data)=='[]'    ...

However, this test does not work as intended, because itArtist.format_cursor_data() will in normal circumstances call_ColorizerInterface._format_cursor_data_override():

defformat_cursor_data(self,data):ifnp.ndim(data)==0andhasattr(self,"_format_cursor_data_override"):returnself._format_cursor_data_override(data)        ...

However, because of the waytest_image_cursor_formatting() is implemented the array sent toim.format_cursor_data() is 1d, and_format_cursor_data_override() is therefore not called.

i.e. this test does not test the formatting of masked image data as intended.

The relevant behavior has another test

The relevant test (test_image.test_image_cursor_formatting()) is 6 years old. Since then, a more comprehensive test forim.format_cursor_data() has been developed, reproduced below.

@pytest.mark.parametrize("data, text", [        ([[10001,10000]],"[10001.000]"),        ([[.123,.987]],"[0.123]"),        ([[np.nan,1,2]],"[]"),        ([[1,1+1e-15]],"[1.0000000000000000]"),        ([[-1,-1]],"[-1.0]"),        ([[0,0]],"[0.00]"),    ])deftest_format_cursor_data(data,text):frommatplotlib.backend_basesimportMouseEventfig,ax=plt.subplots()im=ax.imshow(data)xdisp,ydisp=ax.transData.transform([0,0])event=MouseEvent('motion_notify_event',fig.canvas,xdisp,ydisp)assertim.format_cursor_data(im.get_cursor_data(event))==text

This testsim.format_cursor_data() with masked values (nan), and I therefore believe it is not necessary to adapttest_image.test_image_cursor_formatting() so that it tests the relevant behavior, andim.format_cursor_data() can instead be removed.

Why did this attract my attention

I noticed this because I am adapting_format_cursor_data_override() to work with multivariate data, see#29876 and related PRs, and need to develop new tests for this behavior. I attempted to base my tests ontest_image.test_image_cursor_formatting() but this proved futile, and I will instead implement tests based ontest_image.test_format_cursor_data().

removed test_image_cursor_formatting()

1f2ca75

This test does not test im.format_cursor_data() because it test it with 1d arrays, whereas the artist.format_cursor_data() should forward to colrizingArtist._format_cursor_data_override() but this only happens with 0d data. The correct behavior with nans is tested in the existing test test_format_cursor_data(), so the test removed here, even if working as intended, is superfluous.