REF: Refactor pandas.util.testing to not use pytest at top-level (#16088)

Closes #16088

Author: TomAugspurger

pandas/tests/io/parser/test_network.py

@@ -22,7 +22,8 @@ def salaries_table():
 @pytest.mark.parametrize(
     "compression,extension",
     [('gzip', '.gz'), ('bz2', '.bz2'), ('zip', '.zip'),
-     tm._mark_skipif_no_lzma(('xz', '.xz'))])
+     pytest.mark.skipif(not tm._check_if_lzma(),
+                        reason='need backports.lzma to run')(('xz', '.xz'))])
 @pytest.mark.parametrize('mode', ['explicit', 'infer'])
 @pytest.mark.parametrize('engine', ['python', 'c'])
 def test_compressed_urls(salaries_table, compression, extension, mode, engine):

pandas/util/testing.py

@@ -19,7 +19,6 @@
 from distutils.version import LooseVersion
 
 from numpy.random import randn, rand
-import pytest
 import numpy as np
 
 import pandas as pd
@@ -52,7 +51,13 @@
 
 from pandas.util import libtesting
 from pandas.io.common import urlopen
-slow = pytest.mark.slow
+try:
+    import pytest
+    slow = pytest.mark.slow
+except ImportError:
+    # Should be ok to just ignore. If you actually need
+    # slow then you'll hit an import error long before getting here.
+    pass
 
 
 N = 30
@@ -347,15 +352,10 @@ def _check_if_lzma():
 
 
 def _skip_if_no_lzma():
+    import pytest
     return _check_if_lzma() or pytest.skip('need backports.lzma to run')
 
 
-_mark_skipif_no_lzma = pytest.mark.skipif(
-    not _check_if_lzma(),
-    reason='need backports.lzma to run'
-)
-
-
 def _skip_if_no_xarray():
     try:
         import xarray