TST: Skip tests that use a large amount of memory by default

According to memray, these tests use fairly large amounts of memory:
- lib/matplotlib/tests/test_simplification.py::test_throw_rendering_complexity_exceeded: 2.2GiB
- lib/matplotlib/tests/test_agg.py::test_chunksize_fails: 2.0GiB
- lib/matplotlib/tests/test_image.py::test_large_image[png-col-16777216-2\\*\\*24 rows-upper]: 1.0GiB
- lib/matplotlib/tests/test_image.py::test_large_image[png-col-16777216-2\\*\\*24 rows-lower]: 1.0GiB
- lib/matplotlib/tests/test_image.py::test_downsample_interpolation_stage[png]: 1.0GiB
- lib/matplotlib/tests/test_lines.py::test_invisible_Line_rendering: 822.0MiB
- lib/matplotlib/tests/test_image.py::test_large_image[png-row-8388608-2\\*\\*23 columns-lower]: 537.8MiB
- lib/matplotlib/tests/test_image.py::test_large_image[png-row-8388608-2\\*\\*23 columns-upper]: 537.8MiB

The next closest tests use just 216MiB, then 145.5MiB, etc. and then the
majority under 100MiB.

If you're unlucky, with 4-way xdist you might use upwards of 6GiB RAM if
you get all these on separate processes.

The above tests are all fairly low-level checks for Agg renderer limits
that are not likely to change often, so skip them by default unless on
CI.

Author: QuLogic

doc/devel/testing.rst

@@ -50,6 +50,7 @@ In the root directory of your development repository run::
 ``-n NUM``                     Run tests in parallel over NUM
                                processes (requires pytest-xdist_)
 ``--capture=no`` or ``-s``     Do not capture stdout
+``--high-memory``              Enable tests that use a large amount of memory (>0.5GiB)
 =============================  ===========
 
 To run a single test from the command line, you can provide a file path, optionally

lib/matplotlib/testing/conftest.py

@@ -4,6 +4,17 @@
 from matplotlib import _api
 
 
+def pytest_addoption(parser):
+    from matplotlib.testing import is_ci_environment
+
+    if not hasattr(pytest_addoption, 'called'):
+        parser.addoption('--high-memory', action='store_true', dest='high_memory',
+                         default=is_ci_environment(),
+                         help='enable tests using large amounts of memory')
+        # Ensure we don't get called twice if loaded from matplotlib+mpl_toolkits.
+        pytest_addoption.called = True
+
+
 def pytest_configure(config):
     # config is initialized here rather than in pytest.ini so that `pytest
     # --pyargs matplotlib` (which would not find pytest.ini) works.  The only
@@ -80,6 +91,13 @@ def mpl_test_settings(request):
                 matplotlib.use(prev_backend)
 
 
+@pytest.fixture
+def high_memory(pytestconfig):
+    if not pytestconfig.getoption('high_memory'):
+        pytest.skip('Test uses too much memory')
+    yield
+
+
 @pytest.fixture
 def pd():
     """

lib/matplotlib/tests/conftest.py

@@ -1,2 +1,3 @@
 from matplotlib.testing.conftest import (  # noqa
-    mpl_test_settings, pytest_configure, pytest_unconfigure, pd, text_placeholders, xr)
+    pytest_addoption, pytest_configure, pytest_unconfigure,
+    high_memory, mpl_test_settings, pd, text_placeholders, xr)

lib/matplotlib/tests/test_agg.py

@@ -320,7 +320,7 @@ def test_draw_path_collection_error_handling():
         fig.canvas.draw()
 
 
-def test_chunksize_fails():
+def test_chunksize_fails(high_memory):
     # NOTE: This test covers multiple independent test scenarios in a single
     #       function, because each scenario uses ~2GB of memory and we don't
     #       want parallel test executors to accidentally run multiple of these

lib/matplotlib/tests/test_image.py

@@ -1547,7 +1547,7 @@ def test_upsample_interpolation_stage(fig_test, fig_ref):
 
 
 @check_figures_equal()
-def test_downsample_interpolation_stage(fig_test, fig_ref):
+def test_downsample_interpolation_stage(fig_test, fig_ref, high_memory):
     """
     Show that interpolation_stage='auto' gives the same as 'rgba'
     for downsampling.
@@ -1583,7 +1583,7 @@ def test_rc_interpolation_stage():
     'dim, size, msg', [['row', 2**23, r'2\*\*23 columns'],
                        ['col', 2**24, r'2\*\*24 rows']])
 @check_figures_equal()
-def test_large_image(fig_test, fig_ref, dim, size, msg, origin):
+def test_large_image(fig_test, fig_ref, dim, size, msg, origin, high_memory):
     # Check that Matplotlib downsamples images that are too big for AGG
     # See issue #19276. Currently the fix only works for png output but not
     # pdf or svg output.

lib/matplotlib/tests/test_lines.py

@@ -34,7 +34,7 @@ def test_segment_hits():
 # Runtimes on a loaded system are inherently flaky. Not so much that a rerun
 # won't help, hopefully.
 @pytest.mark.flaky(reruns=5)
-def test_invisible_Line_rendering():
+def test_invisible_Line_rendering(high_memory):
     """
     GitHub issue #1256 identified a bug in Line.draw method
 

lib/matplotlib/tests/test_simplification.py

@@ -455,7 +455,7 @@ def test_start_with_moveto():
     assert segs[0][1] == Path.MOVETO
 
 
-def test_throw_rendering_complexity_exceeded():
+def test_throw_rendering_complexity_exceeded(high_memory):
     plt.rcParams['path.simplify'] = False
     xx = np.arange(2_000_000)
     yy = np.random.rand(2_000_000)

lib/mpl_toolkits/axes_grid1/tests/conftest.py

@@ -1,2 +1,3 @@
-from matplotlib.testing.conftest import (mpl_test_settings,  # noqa
-                                         pytest_configure, pytest_unconfigure)
+from matplotlib.testing.conftest import (  # noqa
+    pytest_addoption, pytest_configure, pytest_unconfigure,
+    high_memory, mpl_test_settings)

lib/mpl_toolkits/axisartist/tests/conftest.py

@@ -1,2 +1,3 @@
-from matplotlib.testing.conftest import (mpl_test_settings,  # noqa
-                                         pytest_configure, pytest_unconfigure)
+from matplotlib.testing.conftest import (  # noqa
+    pytest_addoption, pytest_configure, pytest_unconfigure,
+    high_memory, mpl_test_settings)

lib/mpl_toolkits/mplot3d/tests/conftest.py

@@ -1,2 +1,3 @@
-from matplotlib.testing.conftest import (mpl_test_settings,  # noqa
-                                         pytest_configure, pytest_unconfigure)
+from matplotlib.testing.conftest import (  # noqa
+    pytest_addoption, pytest_configure, pytest_unconfigure,
+    high_memory, mpl_test_settings)