Matplotlib 3.0.3 test_determinism_all fails on RHEL8 s390x

I’m working on updating the EPEL8 matplotlib 3.0.3 package to support wx and am running into a test failure just on s390x:

+ MPLCONFIGDIR=/home/linux1/rpmbuild/BUILD/matplotlib-3.0.3
+ MATPLOTLIBDATA=/home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/share/matplotlib/mpl-data
+ MATPLOTLIBRC=/home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/etc/matplotlibrc
+ PYTHONPATH=/home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages
+ PYTHONDONTWRITEBYTECODE=1
+ xvfb-run -a -s '-screen 0 640x480x24' /usr/libexec/platform-python tests.py -ra -n 2 -m 'not network' -k 'not test_invisible_Line_rendering and not backend_qt5 and not test_tinypages'
Python byte-compilation optimization level: 0
/home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/__init__.py:1460: UserWarning: Matplotlib is not built with the correct FreeType version to run tests.  Set local_freetype=True in setup.cfg and rebuild. Expect many image comparison failures below. Expected freetype version 2.6.1. Found freetype version 2.9.1. Freetype build type is not local
  "" if ft2font.__freetype_build_type__ == 'local' else "not "
=========================================================================================================== test session starts ============================================================================================================
platform linux -- Python 3.6.8, pytest-3.4.2, py-1.5.3, pluggy-0.6.0
rootdir: /home/linux1/rpmbuild/BUILD/matplotlib-3.0.3, inifile: pytest.ini
plugins: xdist-1.24.1, forked-1.0.2
gw0 ok / gw1 ok/home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/__init__.py:1460: UserWarning: Matplotlib is not built with the correct FreeType version to run tests.  Set local_freetype=True in setup.cfg and rebuild. Expect many image comparison failures below. Expected freetype version 2.6.1. Found freetype version 2.9.1. Freetype build type is not local
  "" if ft2font.__freetype_build_type__ == 'local' else "not "
/home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/__init__.py:1460: UserWarning: Matplotlib is not built with the correct FreeType version to run tests.  Set local_freetype=True in setup.cfg and rebuild. Expect many image comparison failures below. Expected freetype version 2.6.1. Found freetype version 2.9.1. Freetype build type is not local
  "" if ft2font.__freetype_build_type__ == 'local' else "not "
gw0 [7567] / gw1 [7567]
scheduling tests via LoadScheduling
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========================================================================================================= short test summary info ==========================================================================================================
FAIL tests/test_backend_pdf.py::test_determinism_all
SKIP [2] /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_animation.py:147: writer 'ffmpeg' not available on this system
SKIP [2] /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_animation.py:147: writer 'avconv' not available on this system
SKIP [2] /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_animation.py:147: writer 'ffmpeg_file' not available on this system
SKIP [2] /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_animation.py:147: writer 'avconv_file' not available on this system
SKIP [2] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_animation.py:212: animation writer not installed
SKIP [2] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_animation.py:226: animation writer not installed
SKIP [616] /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/testing/compare.py:308: Don't know how to convert pdf files to png
SKIP [614] /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/testing/compare.py:308: Don't know how to convert svg files to png
SKIP [3] /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_axes.py:131: Fall out from a fixed numpy bug
SKIP [12] /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/testing/conftest.py:92: could not import 'pandas'
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_pdf.py:195: This test needs a TeX installation
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_pdf.py:224: This test needs a TeX installation
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_pgf.py:85: xelatex + pgf is required
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_pgf.py:116: pdflatex + pgf is required
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_pgf.py:161: xelatex + pgf is required
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_pgf.py:197: pdflatex + pgf is required
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_pgf.py:250: lualatex + pgf is required
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_ps.py:27: This test needs a ghostscript installation
SKIP [2] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_ps.py:27: This test needs a TeX installation
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_ps.py:81: This test needs a ghostscript installation
SKIP [3] /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/testing/compare.py:308: Don't know how to convert eps files to png
SKIP [12] /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_qt4.py:35: Failed to import a Qt4 binding.
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_pgf.py:97: pdflatex + pgf is required
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_pgf.py:144: xelatex + pgf is required
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_pgf.py:176: xelatex + pgf is required
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_pgf.py:223: xelatex + pgf is required
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_ps.py:116: This test needs a ghostscript installation
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_ps.py:131: This test needs a TeX installation
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_svg.py:125: This test needs a TeX installation
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_svg.py:162: This test needs a TeX installation
SKIP [2] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backends_interactive.py:111: Missing dependency
SKIP [1] /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backends_interactive.py:125: could not import 'tornado'
SKIP [1] /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_mlab.py:2172: could not import 'mpl_toolkits.natgrid'
SKIP [1] /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_pyplot.py:15: boilerplate.py not found
SKIP [2] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_usetex.py:8: Missing TeX or Ghostscript or dvipng
SKIP [1] ../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_text.py:465: This test needs a TeX installation
XFAIL tests/test_animation.py::test_failing_ffmpeg
XFAIL tests/test_category.py::TestPlotTypes::()::test_mixed_type_exception[mixed-plot]
XFAIL tests/test_category.py::TestPlotTypes::()::test_mixed_type_exception[string integer-plot]
XFAIL tests/test_category.py::TestPlotTypes::()::test_mixed_type_update_exception[mixed-plot]
XFAIL tests/test_category.py::TestPlotTypes::()::test_mixed_type_update_exception[string integer-plot]
XFAIL tests/test_category.py::TestPlotTypes::()::test_mixed_type_exception[number integer-plot]
XFAIL tests/test_category.py::TestPlotTypes::()::test_mixed_type_exception[missing-plot]
XFAIL tests/test_category.py::TestPlotTypes::()::test_mixed_type_update_exception[number integer-plot]
XFAIL tests/test_category.py::TestPlotTypes::()::test_mixed_type_update_exception[missing-plot]
XFAIL tests/test_patheffects.py::test_PathEffect_points_to_pixels
XPASS tests/test_category.py::TestPlotTypes::()::test_mixed_type_exception[number integer-bar] 
XPASS tests/test_category.py::TestPlotTypes::()::test_mixed_type_exception[missing-bar] 
XPASS tests/test_category.py::TestPlotTypes::()::test_mixed_type_update_exception[number integer-bar] 
XPASS tests/test_category.py::TestPlotTypes::()::test_mixed_type_update_exception[missing-bar] 
XPASS tests/test_category.py::TestPlotTypes::()::test_mixed_type_exception[mixed-bar] 
XPASS tests/test_category.py::TestPlotTypes::()::test_mixed_type_exception[string integer-bar] 
XPASS tests/test_category.py::TestPlotTypes::()::test_mixed_type_update_exception[mixed-bar] 
XPASS tests/test_category.py::TestPlotTypes::()::test_mixed_type_update_exception[string integer-bar] 
XPASS tests/test_tightlayout.py::test_tight_layout4[png] Mismatched version of freetype. Test requires '('2.5.5', '2.6.1')', you have '2.9.1'
================================================================================================================= FAILURES =================================================================================================================
___________________________________________________________________________________________________________ test_determinism_all ___________________________________________________________________________________________________________
[gw0] linux -- Python 3.6.8 /usr/libexec/platform-python

    def test_determinism_all():
        """Test for reproducible PDF output"""
>       _determinism_check(format="pdf")

../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/tests/test_backend_pdf.py:166: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

objects = 'mhi', format = 'pdf', usetex = False

    def _determinism_check(objects='mhi', format="pdf", usetex=False):
        """
        Output three times the same graphs and checks that the outputs are exactly
        the same.
    
        Parameters
        ----------
        objects : str
            contains characters corresponding to objects to be included in the test
            document: 'm' for markers, 'h' for hatch patterns, 'i' for images. The
            default value is "mhi", so that the test includes all these objects.
        format : str
            format string. The default value is "pdf".
        """
        plots = []
        for i in range(3):
            result = subprocess.check_output([
                sys.executable, '-R', '-c',
                'import matplotlib; '
                'matplotlib._called_from_pytest = True; '
                'matplotlib.use(%r); '
                'from matplotlib.testing.determinism import _determinism_save;'
                '_determinism_save(%r, %r, %r)'
                % (format, objects, format, usetex)])
            plots.append(result)
        for p in plots[1:]:
            if usetex:
                if p != plots[0]:
                    pytest.skip("failed, maybe due to ghostscript timestamps")
            else:
>               assert p == plots[0]
E               AssertionError

../../BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/testing/determinism.py:101: AssertionError
============================================================================================================= warnings summary =============================================================================================================
tests/test_image.py::test_full_invalid
  /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/image.py:395: UserWarning: Warning: converting a masked element to nan.
    dv = (np.float64(self.norm.vmax) -
  /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/image.py:396: UserWarning: Warning: converting a masked element to nan.
    np.float64(self.norm.vmin))
  /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/image.py:403: UserWarning: Warning: converting a masked element to nan.
    a_min = np.float64(newmin)
  /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/image.py:408: UserWarning: Warning: converting a masked element to nan.
    a_max = np.float64(newmax)
  /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/colors.py:918: UserWarning: Warning: converting a masked element to nan.
    dtype = np.min_scalar_type(value)
  /usr/lib64/python3.6/site-packages/numpy/ma/core.py:716: UserWarning: Warning: converting a masked element to nan.
    data = np.array(a, copy=False, subok=subok)

tests/test_style.py::test_alias[mpl20]
  /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/__init__.py:874: MatplotlibDeprecationWarning: 
  examples.directory is deprecated; in the future, examples will be found relative to the 'datapath' directory.
    "found relative to the 'datapath' directory.".format(key))
  /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/__init__.py:874: MatplotlibDeprecationWarning: 
  examples.directory is deprecated; in the future, examples will be found relative to the 'datapath' directory.
    "found relative to the 'datapath' directory.".format(key))

tests/test_style.py::test_alias[mpl15]
  /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/__init__.py:874: MatplotlibDeprecationWarning: 
  examples.directory is deprecated; in the future, examples will be found relative to the 'datapath' directory.
    "found relative to the 'datapath' directory.".format(key))
  /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/__init__.py:874: MatplotlibDeprecationWarning: 
  examples.directory is deprecated; in the future, examples will be found relative to the 'datapath' directory.
    "found relative to the 'datapath' directory.".format(key))

tests/test_axisartist_axislines.py::test_Axes
  /home/linux1/rpmbuild/BUILDROOT/python-matplotlib-3.0.3-3.el8.s390x/usr/lib64/python3.6/site-packages/matplotlib/figure.py:445: UserWarning: Matplotlib is currently using agg, which is a non-GUI backend, so cannot show the figure.
    % get_backend())

-- Docs: http://doc.pytest.org/en/latest/warnings.html
======================================================================== 1 failed, 6248 passed, 1299 skipped, 10 xfailed, 9 xpassed, 11 warnings in 143.36 seconds =========================================================================

I’ve poked at it a bit and matplotlib is able to produce the pdf output. Any idea what might trigger the difference?