Create skip_if_no helper function to skip tests when missing a package (

#2883)

Add a helper testing function which returns a pytest.mark.skipif mark
that will skip certain unit tests when a package is not installed. This is
adapted from pandas' internal skip_if_no function at
https://github.com/pandas-dev/pandas/blob/v2.1.4/pandas/util/_test_decorators.py#L121.
Added a unit test to ensure that a correct pytest mark is returned.

---------

Co-authored-by: Dongdong Tian <[email protected]>

pygmt/helpers/testing.py

@@ -1,10 +1,12 @@
 """
 Helper functions for testing.
 """
+import importlib
 import inspect
 import os
 import string
 
+import pytest
 from pygmt.exceptions import GMTImageComparisonFailure
 from pygmt.io import load_dataarray
 from pygmt.src import which
@@ -237,3 +239,42 @@ def load_static_earth_relief():
  """
  fname = which("@static_earth_relief.nc", download="c")
  return load_dataarray(fname)
+
+
+def skip_if_no(package):
+ """
+ Generic function to help skip tests when required packages are not present
+ on the testing system.
+
+ This function returns a pytest mark with a skip condition that will be
+ evaluated during test collection. An attempt will be made to import the
+ specified ``package``.
+
+ The mark can be used as either a decorator for a test class or to be
+ applied to parameters in pytest.mark.parametrize calls or parametrized
+ fixtures. Use pytest.importorskip if an imported moduled is later needed
+ or for test functions.
+
+ If the import is unsuccessful, then the test function (or test case when
+ used in conjunction with parametrization) will be skipped.
+
+ Adapted from
+ https://github.com/pandas-dev/pandas/blob/v2.1.4/pandas/util/_test_decorators.py#L121
+
+ Parameters
+ ----------
+ package : str
+ The name of the required package.
+
+ Returns
+ -------
+ pytest.MarkDecorator
+ A pytest.mark.skipif to use as either a test decorator or a
+ parametrization mark.
+ """
+ try:
+ _ = importlib.import_module(name=package)
+ has_package = True
+ except ImportError:
+ has_package = False
+ return pytest.mark.skipif(not has_package, reason=f"Could not import '{package}'")

pygmt/tests/test_helpers.py

@@ -15,7 +15,7 @@
  kwargs_to_strings,
  unique_name,
 )
-from pygmt.helpers.testing import load_static_earth_relief
+from pygmt.helpers.testing import load_static_earth_relief, skip_if_no
 
 
 def test_load_static_earth_relief():
@@ -147,3 +147,19 @@ def test_args_in_kwargs():
  # Failing list of arguments
  failing_args = ["D", "E", "F"]
  assert not args_in_kwargs(args=failing_args, kwargs=kwargs)
+
+
+def test_skip_if_no():
+ """
+ Test that the skip_if_no helper testing function returns a
+ pytest.mask.skipif mark decorator.
+ """
+ # Check pytest.mark with a dependency that can be imported
+ mark_decorator = skip_if_no(package="numpy")
+ assert mark_decorator.args[0] is False
+
+ # Check pytest.mark with a dependency that cannot be imported
+ mark_decorator = skip_if_no(package="nullpackage")
+ assert mark_decorator.args[0] is True
+ assert mark_decorator.kwargs["reason"] == "Could not import 'nullpackage'"
+ assert mark_decorator.markname == "skipif"