Use AssertPrints in tests for autoreload extension.

IPython/extensions/tests/test_autoreload.py

@@ -7,6 +7,7 b' import time'
 from StringIO import StringIO
 
 import nose.tools as nt
+import IPython.testing.tools as tt
 
 from IPython.extensions.autoreload import AutoreloadInterface
 from IPython.core.hooks import TryNext
@@ -197,19 +198,11 b" class Bar: # old-style class: weakref doesn't work for it on Python < 2.7"
 a syntax error
 """)
 
-        old_stderr = sys.stderr
-        new_stderr = StringIO()
-        sys.stderr = new_stderr
-        try:
+        with tt.AssertPrints(('[autoreload of %s failed:' % mod_name), channel='stderr'):
             self.shell.run_code("pass") # trigger reload
+        with tt.AssertNotPrints(('[autoreload of %s failed:' % mod_name), channel='stderr'):
             self.shell.run_code("pass") # trigger another reload
-            check_module_contents()
-        finally:
-            sys.stderr = old_stderr
-
-        nt.assert_true(('[autoreload of %s failed:' % mod_name) in
-                       new_stderr.getvalue())
-        nt.assert_equal(new_stderr.getvalue().count('[autoreload of'), 1)
+        check_module_contents()
 
         #
         # Rewrite module (this time reload should succeed)

IPython/testing/tools.py

@@ -342,22 +342,23 b' class AssertPrints(object):'
     
     Examples
     --------
-    >>> with AssertPrints("abc"):
+    >>> with AssertPrints("abc", suppress=False):
     ...     print "abcd"
     ...     print "def"
     ... 
     abcd
     def
     """
-    def __init__(self, s, channel='stdout'):
+    def __init__(self, s, channel='stdout', suppress=True):
         self.s = s
         self.channel = channel
+        self.suppress = suppress
     
     def __enter__(self):
         self.orig_stream = getattr(sys, self.channel)
         self.buffer = MyStringIO()
         self.tee = Tee(self.buffer, channel=self.channel)
-        setattr(sys, self.channel, self.tee)
+        setattr(sys, self.channel, self.buffer if self.suppress else self.tee)
     
     def __exit__(self, etype, value, traceback):
         self.tee.flush()
@@ -365,6 +366,17 b' class AssertPrints(object):'
         printed = self.buffer.getvalue()
         assert self.s in printed, notprinted_msg.format(self.s, self.channel, printed)
         return False
+    
+class AssertNotPrints(AssertPrints):
+    """Context manager for checking that certain output *isn't* produced.
+    
+    Counterpart of AssertPrints"""
+    def __exit__(self, etype, value, traceback):
+        self.tee.flush()
+        setattr(sys, self.channel, self.orig_stream)
+        printed = self.buffer.getvalue()
+        assert self.s not in printed, notprinted_msg.format(self.s, self.channel, printed)
+        return False
 
 @contextmanager
 def mute_warn():