Let the examples be skipped if resources aren't around.

examples/concurrent_download.py

 #!/usr/bin/python
 # Copyright (c) 2009 Denis Bilenko. See LICENSE for details.
-
+# gevent-test-requires-resource: network
 """Spawn multiple workers and wait for them to complete"""
 from __future__ import print_function
 import gevent

examples/dns_mass_resolve.py

 #!/usr/bin/python
+# gevent-test-requires-resource: network
 """Resolve hostnames concurrently, exit after 2 seconds.
 
 Under the hood, this might use an asynchronous resolver based on

examples/geventsendfile.py

@@ -2,6 +2,7 @@
 
 [1] http://pypi.python.org/pypi/py-sendfile/
 """
+# gevent-test-requires-resource: sendfile
 # pylint:disable=import-error
 from errno import EAGAIN
 from sendfile import sendfile as original_sendfile

examples/psycopg2_pool.py

 from __future__ import print_function
+# gevent-test-requires-resource: psycopg2
 # pylint:disable=import-error,broad-except,bare-except
 import sys
 import contextlib

examples/unixsocket_client.py

 from __future__ import print_function
+# gevent-test-requires-resource: unixsocket_server
 import socket
 
 s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)

examples/unixsocket_server.py

+# gevent-test-requires-resource: unixsocket_client
 import os
 from gevent.pywsgi import WSGIServer
 from gevent import socket

examples/webpy.py

 #!/usr/bin/python
+# gevent-test-requires-resource: webpy
 """A web.py application powered by gevent"""
 
 from __future__ import print_function

src/gevent/testing/resources.py

@@ -171,6 +171,15 @@ def setup_resources(resources=None):
 
     return resources
 
+def ensure_setup_resources():
+    # Call when you don't know if resources have been setup and you want to
+    # get the environment variable if needed.
+    # Returns an object with `is_resource_enabled`.
+    from . import support
+    if not support.gevent_has_setup_resources:
+        setup_resources()
+
+    return support
 
 def exit_without_resource(resource):
     """
@@ -178,15 +187,22 @@ def exit_without_resource(resource):
 
     Exits with a status of 0 if the resource isn't enabled.
     """
-    from . import support
-    if not support.gevent_has_setup_resources:
-        setup_resources()
 
-    if not support.is_resource_enabled(resource):
+    if not ensure_setup_resources().is_resource_enabled(resource):
         print("Skipped: %r not enabled" % (resource,))
         import sys
         sys.exit(0)
 
+def skip_without_resource(resource, reason=''):
+    requires = 'Requires resource %r' % (resource,)
+    if not reason:
+        reason = requires
+    else:
+        reason = reason + ' (' + requires + ')'
+
+    if not ensure_setup_resources().is_resource_enabled(resource):
+        import unittest
+        raise unittest.SkipTest(reason)
 
 if __name__ == '__main__':
     print(setup_resources())

src/gevent/testing/skipping.py

@@ -172,16 +172,11 @@ def skipWithoutResource(resource, reason=''):
     else:
         reason = reason + ' (' + requires + ')'
 
-
     # Defer until runtime; resources are established as part
     # of test startup.
     def predicate(): # This is easily cached if needed
-        from . import support
-        if not support.gevent_has_setup_resources:
-            # In this case, nothing to do but pull from the environment
-            from . import resources
-            resources.setup_resources()
-        return support.is_resource_enabled(resource)
+        from . import resources
+        return resources.ensure_setup_resources().is_resource_enabled(resource)
 
     return _make_runtime_skip_decorator(reason, predicate)
 

src/gevent/tests/test__examples.py

+"""
+Test the contents of the ``examples/`` directory.
+
+If an existing test in *this* directory named ``test__example_<fn>.py`` exists,
+where ``<fn>`` is the base filename of an example file, it will not be tested
+here.
+
+Examples can specify that they need particular test resources to be enabled
+by commenting (one per line) ``# gevent-test-requires-resource: <resource>``;
+most commonly the resource will be ``network``. You can use this technique to specify
+non-existant resources for things that should never be tested.
+"""
+import re
 import sys
 import os
 import glob
@@ -9,23 +22,17 @@ from gevent.testing import util
 
 this_dir = os.path.dirname(__file__)
 
-# XXX: Review these, check those that use external network resources
-# and exclude if that resource is disabled.
-
 def _find_files_to_ignore():
     old_dir = os.getcwd()
     try:
         os.chdir(this_dir)
 
+        # These three are all tested with test___example_servers.
+        # TODO: Refactor those to regular test__example_*foo* files.
         result = [
             'wsgiserver.py',
             'wsgiserver_ssl.py',
             'webproxy.py',
-            'webpy.py',
-            'unixsocket_server.py',
-            'unixsocket_client.py',
-            'psycopg2_pool.py',
-            'geventsendfile.py',
         ]
         if greentest.PYPY and greentest.RUNNING_ON_APPVEYOR:
             # For some reason on Windows with PyPy, this times out,
@@ -48,7 +55,21 @@ class _AbstractTestMixin(util.ExampleMixin):
     time_range = (2, 4)
     filename = None
 
+    def _check_resources(self):
+        from gevent.testing import resources
+
+        with open(os.path.join(self.cwd, self.filename), 'r') as f:
+            contents = f.read()
+
+        pattern = re.compile('^# gevent-test-requires-resource: (.*)$', re.MULTILINE)
+        resources_needed = re.finditer(pattern, contents)
+        for match in resources_needed:
+            needed = contents[match.start(1):match.end(1)]
+            resources.skip_without_resource(needed)
+
     def test_runs(self):
+        self._check_resources()
+
         start = time.time()
         min_time, max_time = self.time_range
         if not util.run([sys.executable, '-u', self.filename],
@@ -76,6 +97,7 @@ def _build_test_classes():
         bn = os.path.basename(filename)
         if bn in ignore:
             continue
+
         tc = type(
             'Test_' + bn,
             (_AbstractTestMixin, greentest.TestCase),