$ ls ~/matplotlib-env/
ls: cannot access '~/matplotlib-env/': No such file or directory
$ python3 -mvenv ~/matplotlib-env/
$ source ~/matplotlib-env/bin/activate
$ python -mpip install -ve .
[...]
Successfully installed cycler-0.10.0 kiwisolver-1.1.0 matplotlib numpy-1.17.4 pillow-6.2.1 pyparsing-2.4.5 python-dateutil-2.8.1 six-1.13.0
Cleaning up...
Removed build tracker '/tmp/pip-req-tracker-aczpokn_'
$ pip install pytest
[...]
Successfully installed attrs-19.3.0 importlib-metadata-1.3.0 more-itertools-8.0.2 packaging-19.2 pluggy-0.13.1 py-1.8.0 pytest-5.3.2 wcwidth-0.1.7 zipp-0.6.0
$ python -mpytest --maxfail=1
[...]
E           FileNotFoundError: [Errno 2] No such file or directory: '/path/to/source/result_images/test_arrow_patches/fancyarrow_test_image-expected_svg.png'

fancyarrow_test_image-expected_pdf.png
fancyarrow_test_image-expected.png
fancyarrow_test_image-expected.svg
fancyarrow_test_image.pdf
fancyarrow_test_image_pdf.png
fancyarrow_test_image.png
fancyarrow_test_image.svg

$ python --version
Python 3.7.5

$ python -c "import matplotlib; print(matplotlib.__version__)"
3.1.1.post2790+gce7115d3d

$ inkscape --version
Inkscape 1.0beta1 (fe3e306978, 2019-09-17)