DOC: fill in the rest of the optional test dependencies

Also moves inkscape and gs to "optional" testing section because the tests
will run with out them (but it will skip the ps / eps / svg tests)

Co-authored-by: Tim Hoffmann <[email protected]>

Author: tacaswell

doc/devel/dependencies.rst

@@ -183,32 +183,55 @@ This section lists the additional software required for
 Required:
 
 - pytest_ (>=3.6)
-- Ghostscript_ (>= 9.0, to render PDF files)
-- Inkscape_ (to render SVG files)
-
-  .. note::
-
-    When installing Inkscape on Windows, make sure that you select Add
-    Inkscape to system PATH, either for all users or current user, or the
-    tests will not find it.
 
 Optional:
 
+In addition to all of the optional dependencies on the main library, for
+testing the following will be used if they are installed.
+
+- Ghostscript_ (>= 9.0, to render PDF files)
+- Inkscape_ (to render SVG files)
+- nbformat_ and nbconvert_ used to test the notebook backend
+- pandas_ used to test compatibility with Pandas
+- pikepdf_ used in some tests for the pgf and pdf backends
+- psutil_ used in testing the interactive backends
 - pytest-cov_ (>=2.3.1) to collect coverage information
 - pytest-flake8_ to test coding standards using flake8_
 - pytest-timeout_ to limit runtime in case of stuck tests
 - pytest-xdist_ to run tests in parallel
 - pytest-xvfb_ to run tests without windows popping up (Linux)
+- pytz_ used to test pytz int
+- sphinx_ used to test our sphinx extensions
+- WenQuanYi Zen Hei and `Noto Sans CJK <https://fonts.google.com/noto/use>`_
+  fonts for testing font fallback and non-western fonts
+- xarray_ used to test compatibility with xarray
+
+If any of these dependencies are not discovered the tests that rely on them
+will be skipped by pytest.
+
+.. note::
+
+  When installing Inkscape on Windows, make sure that you select “Add
+  Inkscape to system PATH”, either for all users or current user, or the
+  tests will not find it.
 
-.. _pytest: http://doc.pytest.org/en/latest/
 .. _Ghostscript: https://www.ghostscript.com/
 .. _Inkscape: https://inkscape.org
+.. _flake8: https://pypi.org/project/flake8/
+.. _nbconvert: https://pypi.org/project/nbconvert/
+.. _nbformat: https://pypi.org/project/nbformat/
+.. _pandas: https://pypi.org/project/pandas/
+.. _pikepdf: https://pypi.org/project/pikepdf/
+.. _psutil: https://pypi.org/project/psuitl/
+.. _pytz: https://fonts.google.com/noto/use#faq
 .. _pytest-cov: https://pytest-cov.readthedocs.io/en/latest/
 .. _pytest-flake8: https://pypi.org/project/pytest-flake8/
 .. _pytest-timeout: https://pypi.org/project/pytest-timeout/
 .. _pytest-xdist: https://pypi.org/project/pytest-xdist/
 .. _pytest-xvfb: https://pypi.org/project/pytest-xvfb/
-.. _flake8: https://pypi.org/project/flake8/
+.. _pytest: http://doc.pytest.org/en/latest/
+.. _sphinx: https://pypi.org/project/Sphinx/
+.. _xarray: https://pypi.org/project/xarray/
 
 
 .. _doc-dependencies: