test: workaround intermittent macos CI matplotlib failures (modflowpy…

…#1491), don't use plt.show() in tests, add explanatory comments to conftest.py

autotest/conftest.py

@@ -1,7 +1,5 @@
 import importlib
-import io
 import os
-import pkg_resources
 import socket
 import sys
 from os import environ
@@ -14,6 +12,7 @@
 from urllib import request
 from warnings import warn
 
+import pkg_resources
 import pytest
 
 # constants
@@ -139,7 +138,9 @@ def is_connected(hostname):
 
 
 def is_in_ci():
-    return "CI" in os.environ
+    # if running in GitHub Actions CI, "CI" variable always set to true
+    # https://docs.github.com/en/actions/learn-github-actions/environment-variables#default-environment-variables
+    return bool(os.environ.get("CI", None))
 
 
 def is_github_rate_limited() -> Optional[bool]:
@@ -464,3 +465,12 @@ def run_py_script(script, *args, verbose=False):
     """Run a Python script, return tuple (stdout, stderr, returncode)."""
     return run_cmd(
         sys.executable, script, *args, verbose=verbose, cwd=Path(script).parent)
+
+
+# use noninteractive matplotlib backend if in Mac OS CI to avoid pytest-xdist node failure
+# e.g. https://github.com/modflowpy/flopy/runs/7748574375?check_suite_focus=true#step:9:57
+@pytest.fixture(scope="session", autouse=True)
+def patch_macos_ci_matplotlib():
+    if is_in_ci() and system().lower() == "darwin":
+        import matplotlib
+        matplotlib.use("agg")

autotest/test_binarygrid_util.py

@@ -1,10 +1,19 @@
+from platform import system
+
 import matplotlib
 import numpy as np
 import pytest
-from matplotlib import pyplot as plt
-
 from flaky import flaky
 
+from autotest.conftest import is_in_ci
+
+# use noninteractive backend if in Mac OS CI to avoid occasional pytest-xdist node failure
+# e.g. https://github.com/modflowpy/flopy/runs/7748574375?check_suite_focus=true#step:9:57
+if is_in_ci() and system().lower() == "darwin":
+    matplotlib.use("agg")
+
+from matplotlib import pyplot as plt
+
 from flopy.discretization import StructuredGrid, UnstructuredGrid, VertexGrid
 from flopy.mf6.utils import MfGrdFile
 

autotest/test_sfr.py

@@ -8,8 +8,8 @@
 import matplotlib.pyplot as plt
 import numpy as np
 import pytest
-from autotest.conftest import get_example_data_path, requires_exe, requires_pkg
 
+from autotest.conftest import get_example_data_path, requires_exe, requires_pkg
 from flopy.discretization import StructuredGrid
 from flopy.modflow import Modflow, ModflowDis, ModflowSfr2, ModflowStr
 from flopy.modflow.mfsfr2 import check
@@ -796,11 +796,9 @@ def test_sfr_plot(mf2005_model_path):
     tv = sfr.plot(
         key="strtop",
     )
-    plt.show(block=False)
     assert issubclass(
         type(tv[0]), matplotlib.axes.SubplotBase
     ), "could not plot strtop"
-    plt.close("all")
 
 
 def get_test_matrix():