Merge pull request #2009 from EliahKagan/cygwin-xfail-ci

Mark `test_installation` xfail on Cygwin CI

Author: Byron

test/test_installation.py

@@ -4,11 +4,19 @@
 import ast
 import os
 import subprocess
+import sys
+
+import pytest
 
 from test.lib import TestBase, VirtualEnvironment, with_rw_directory
 
 
 class TestInstallation(TestBase):
+    @pytest.mark.xfail(
+        sys.platform == "cygwin" and "CI" in os.environ,
+        reason="Trouble with pip on Cygwin CI, see issue #2004",
+        raises=subprocess.CalledProcessError,
+    )
     @with_rw_directory
     def test_installation(self, rw_dir):
         venv = self._set_up_venv(rw_dir)