1 files changed, 100 insertions, 5 deletions
diff --git a/tests/util.py b/tests/util.py
index 4ca02374..cdc835c9 100644
--- a/tests/util.py
+++ b/tests/util.py
@@ -1,19 +1,21 @@
 from os.path import dirname, realpath, join
+import os
+import sys
+import unittest
 
 import pytest
 
 from paramiko.py3compat import builtins
+from paramiko.ssh_gss import GSS_AUTH_AVAILABLE
 
 
 def _support(filename):
     return join(dirname(realpath(__file__)), filename)
 
 
-# TODO: consider using pytest.importorskip('gssapi') instead? We presumably
-# still need CLI configurability for the Kerberos parameters, though, so can't
-# JUST key off presence of GSSAPI optional dependency...
-# TODO: anyway, s/True/os.environ.get('RUN_GSSAPI', False)/ or something.
-needs_gssapi = pytest.mark.skipif(True, reason="No GSSAPI to test")
+needs_gssapi = pytest.mark.skipif(
+    not GSS_AUTH_AVAILABLE, reason="No GSSAPI to test"
+)
 
 
 def needs_builtin(name):
@@ -25,3 +27,96 @@ def needs_builtin(name):
 
 
 slow = pytest.mark.slow
+
+# GSSAPI / Kerberos related tests need a working Kerberos environment.
+# The class `KerberosTestCase` provides such an environment or skips all tests.
+# There are 3 distinct cases:
+#
+# - A Kerberos environment has already been created and the environment
+#   contains the required information.
+#
+# - We can use the package 'k5test' to setup an working kerberos environment on
+#   the fly.
+#
+# - We skip all tests.
+#
+# ToDo: add a Windows specific implementation?
+
+if (
+    os.environ.get("K5TEST_USER_PRINC", None)
+    and os.environ.get("K5TEST_HOSTNAME", None)
+    and os.environ.get("KRB5_KTNAME", None)
+):  # add other vars as needed
+
+    # The environment provides the required information
+    class DummyK5Realm(object):
+        def __init__(self):
+            for k in os.environ:
+                if not k.startswith("K5TEST_"):
+                    continue
+                setattr(self, k[7:].lower(), os.environ[k])
+            self.env = {}
+
+    class KerberosTestCase(unittest.TestCase):
+        @classmethod
+        def setUpClass(cls):
+            cls.realm = DummyK5Realm()
+
+        @classmethod
+        def tearDownClass(cls):
+            del cls.realm
+
+
+else:
+    try:
+        # Try to setup a kerberos environment
+        from k5test import KerberosTestCase
+    except Exception:
+        # Use a dummy, that skips all tests
+        class KerberosTestCase(unittest.TestCase):
+            @classmethod
+            def setUpClass(cls):
+                raise unittest.SkipTest(
+                    "Missing extension package k5test. "
+                    'Please run "pip install k5test" '
+                    "to install it."
+                )
+
+
+def update_env(testcase, mapping, env=os.environ):
+    """Modify os.environ during a test case and restore during cleanup."""
+    saved_env = env.copy()
+
+    def replace(target, source):
+        target.update(source)
+        for k in list(target):
+            if k not in source:
+                target.pop(k, None)
+
+    testcase.addCleanup(replace, env, saved_env)
+    env.update(mapping)
+    return testcase
+
+
+def k5shell(args=None):
+    """Create a shell with an kerberos environment
+
+    This can be used to debug paramiko or to test the old GSSAPI.
+    To test a different GSSAPI, simply activate a suitable venv
+    within the shell.
+    """
+    import k5test
+    import atexit
+    import subprocess
+
+    k5 = k5test.K5Realm()
+    atexit.register(k5.stop)
+    os.environ.update(k5.env)
+    for n in ("realm", "user_princ", "hostname"):
+        os.environ["K5TEST_" + n.upper()] = getattr(k5, n)
+
+    if not args:
+        args = sys.argv[1:]
+    if not args:
+        args = [os.environ.get("SHELL", "bash")]
+    sys.exit(subprocess.call(args))