TST: encaplsulate test skipping in a unified function that should wor…

…k on any test runner with any Python version

yt/testing.py

@@ -12,6 +12,7 @@
 
 import matplotlib
 import numpy as np
+import pytest
 from more_itertools import always_iterable
 from numpy.random import RandomState
 from unyt.exceptions import UnitOperationError
@@ -856,6 +857,21 @@ def expand_keywords(keywords, full=False):
     return list_of_kwarg_dicts
 
 
+def skip_case(*, reason: str):
+    """
+    An adapter test skipping function that should work with both test runners
+    (nosetest or pytest) and with any Python version.
+    """
+    if sys.version_info >= (3, 10):
+        # nose isn't compatible with Python 3.10 so we can't import it here
+        pytest.skip(reason)
+    else:
+        # pytest.skip() isn't recognized by nosetest (but nose.SkipTest works in pytest !)
+        from nose import SkipTest
+
+        raise SkipTest(reason)
+
+
 def requires_module(module):
     """
     Decorator that takes a module name as an argument and tries to import it.
@@ -864,12 +880,11 @@ def requires_module(module):
     being imported will not fail if the module is not installed on the testing
     platform.
     """
-    from nose import SkipTest
 
     def ffalse(func):
         @functools.wraps(func)
         def false_wrapper(*args, **kwargs):
-            raise SkipTest
+            skip_case(reason=f"Missing required module {module}")
 
         return false_wrapper
 
@@ -901,8 +916,6 @@ def requires_module_pytest(*module_names):
 
     So that it can be later renamed to `requires_module`.
     """
-    import pytest
-
     from yt.utilities import on_demand_imports as odi
 
     def deco(func):
@@ -930,16 +943,14 @@ def inner_func(*args, **kwargs):
 
 
 def requires_file(req_file):
-    from nose import SkipTest
-
     path = ytcfg.get("yt", "test_data_dir")
 
     def ffalse(func):
         @functools.wraps(func)
         def false_wrapper(*args, **kwargs):
             if ytcfg.get("yt", "internals", "strict_requires"):
                 raise FileNotFoundError(req_file)
-            raise SkipTest
+            skip_case(reason=f"Missing required file {req_file}")
 
         return false_wrapper
 
@@ -1339,7 +1350,6 @@ def requires_backend(backend):
     Decorated function or null function
 
     """
-    import pytest
 
     def ffalse(func):
         # returning a lambda : None causes an error when using pytest. Having
@@ -1350,8 +1360,7 @@ def ffalse(func):
         # exception in the xfail case for that test
         def skip(*args, **kwargs):
             msg = f"`{backend}` backend not in use, skipping: `{func.__name__}`"
-            print(msg, file=sys.stderr)
-            pytest.skip(msg)
+            skip_case(reason=msg)
 
         if ytcfg.get("yt", "internals", "within_pytest"):
             return skip
@@ -1367,8 +1376,6 @@ def ftrue(func):
 
 
 def requires_external_executable(*names):
-    import pytest
-
     def deco(func):
         missing = []
         for name in names:

yt/visualization/tests/test_geo_projections.py

@@ -1,8 +1,6 @@
 import unittest
 
-import pytest
 from nose.plugins.attrib import attr
-from packaging.version import Version
 
 import yt
 from yt.testing import ANSWER_TEST_TAG, fake_amr_ds, requires_module
@@ -134,12 +132,6 @@ def test_projection_object(self):
     def test_nondefault_transform(self):
         from yt.utilities.on_demand_imports import _cartopy as cartopy
 
-        if Version(cartopy.__version__) >= Version("0.19"):
-            # see https://github.com/yt-project/yt/issues/3705
-            pytest.skip(
-                "SlicePlot fails with 'ValueError: Invalid vmin or vmax' (frb is full of nans or infs)"
-            )
-
         axis = "altitude"
         self.ds.coordinates.data_transform[axis] = "Miller"
         self.slc = yt.SlicePlot(self.ds, axis, ("stream", "Density"), origin="native")