Fixed bug in alias; wrote new alias test.

IPython/core/alias.py

@@ -169,6 +169,10 b' class Alias(object):'
         if cmd.find('%l') >= 0:
             cmd = cmd.replace('%l', rest)
             rest = ''
+         
+        if cmd.find('%%s') >= 1:
+            cmd = cmd.replace('%%s', '%s')
+            
         if nargs==0:
             # Simple, argument-less aliases
             cmd = '%s %s' % (cmd, rest)

IPython/core/tests/test_alias.py

@@ -42,9 +42,9 b' def test_alias_args_error():'
     
 def test_alias_args_commented():
     """Check that alias correctly ignores 'commented out' args"""
-    _ip.alias_manager.define_alias('commetarg', 'echo this is %%s a "commented out" arg')
+    _ip.magic('alias commetarg echo this is %%s a "commented out" arg')
     
-    with capture_output as cap:
+    with capture_output() as cap:
         _ip.run_cell('commetarg')
     
     nt.assert_equal(cap.stdout, 'this is %s a "commented out" arg')
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