def fill_gradient(self, canvas, X, percentiles, color=None, label=None, **kwargs):
        print("fill_gradient not implemented in this backend.")
Tests reading then seeking backwards.
dataset/ETHPy150Open SheffieldML/GPy/GPy/plotting/abstract_plotting_library.py/AbstractPlottingLibrary.fill_gradient--crossover with--dataset/ETHPy150Open GoogleCloudPlatform/gsutil/gslib/tests/test_hashing_helper.py/TestHashingFileUploadWrapper._testSeekBack