add an example for testing from an app if a test run is ongoing

--HG--
branch : trunk

doc/example/misc.txt

@@ -0,0 +1,32 @@
+
+Misc examples
+====================================================
+
+Detect if running from within a py.test run
+--------------------------------------------------------------
+
+Usually it is a good idea to make application code
+behave differently if called from a test.  But if you
+absolutely must find out if your application code is 
+running from a test you can do something like this::
+
+    # content of conftest.py in your testing directory
+
+    def pytest_configure(config):
+        import sys   
+        sys._called_from_test = True
+
+    def pytest_unconfigure(config):
+        del sys._called_from_test
+
+and then check for the ``sys._called_from_test`` flag::
+
+    if hasattr(sys, '_called_from_test'):
+        # called from within a test run
+    else:
+        # called "normally"
+    
+accordingly in your application.  It's also a good idea
+to rather use your own application module rather than ``sys``
+for handling flag.
+

doc/examples.txt

@@ -9,3 +9,4 @@ Usages and Examples
 
    example/marking.txt
    example/mysetup.txt
+   example/misc.txt