TST: add td.skip_if_no_NEP18

Author: pilkibun

pandas/compat/numpy/__init__.py

@@ -13,7 +13,10 @@
 _np_version_under1p16 = _nlv < LooseVersion('1.16')
 _np_version_under1p17 = _nlv < LooseVersion('1.17')
 _is_numpy_dev = '.dev' in str(_nlv)
-
+try:
+    _NEP18_enabled = np.core.overrides.ENABLE_ARRAY_FUNCTION
+except Exception:
+    _NEP18_enabled = False
 
 if _nlv < '1.13.3':
     raise ImportError('this version of pandas is incompatible with '

pandas/util/_test_decorators.py

@@ -31,7 +31,7 @@ def test_foo():
 import pytest
 
 from pandas.compat import is_platform_32bit, is_platform_windows
-from pandas.compat.numpy import _np_version
+from pandas.compat.numpy import _NEP18_enabled, _np_version
 
 from pandas.core.computation.expressions import (
     _NUMEXPR_INSTALLED, _USE_NUMEXPR)
@@ -165,6 +165,8 @@ def skip_if_no(
                                    "installed->{installed}".format(
                                        enabled=_USE_NUMEXPR,
                                        installed=_NUMEXPR_INSTALLED))
+skip_if_no_NEP18 = pytest.mark.skipif(not _NEP18_enabled,
+                                      reason="numpy NEP-18 disabled")
 
 
 def skip_if_np_lt(ver_str, reason=None, *args, **kwds):