def makeTestFonts(rootPath):
    path1 = os.path.join(rootPath, "mutingMaster1.ufo")
    path2 = os.path.join(rootPath, "mutingMaster2.ufo")
    path3 = os.path.join(rootPath, "mutedGlyphInstance.ufo")
    # Two masters
    f1 = Font()
    addGlyphs(f1, 0)
    f1.info.unitsPerEm = 1000
    f1.kerning[('glyphOne', 'glyphOne')] = -100
    f2 = Font()
    addGlyphs(f2, 33)
    f2.info.unitsPerEm = 2000
    f2.kerning[('glyphOne', 'glyphOne')] = -200
    # save
    f1.save(path1, 3)
    f2.save(path2, 3)
    return path1, path2, path3
Make some test fonts that have the kerning problem.
dataset/ETHPy150Open LettError/MutatorMath/Lib/mutatorMath/test/ufo/mutingTest.py/makeTestFonts