add regex support to AssertPrints

IPython/testing/tools.py

@@ -327,6 +327,8 b' else:'
             s = py3compat.cast_unicode(s, encoding=DEFAULT_ENCODING)
             super(MyStringIO, self).write(s)
 
+_re_type = type(re.compile(r''))
+
 notprinted_msg = """Did not find {0!r} in printed output (on {1}):
 -------
 {2!s}
@@ -347,7 +349,7 b' class AssertPrints(object):'
     """
     def __init__(self, s, channel='stdout', suppress=True):
         self.s = s
-        if isinstance(self.s, py3compat.string_types):
+        if isinstance(self.s, (py3compat.string_types, _re_type)):
             self.s = [self.s]
         self.channel = channel
         self.suppress = suppress
@@ -366,7 +368,10 b' class AssertPrints(object):'
         setattr(sys, self.channel, self.orig_stream)
         printed = self.buffer.getvalue()
         for s in self.s:
-            assert s in printed, notprinted_msg.format(s, self.channel, printed)
+            if isinstance(s, _re_type):
+                assert s.search(printed), notprinted_msg.format(s.pattern, self.channel, printed)
+            else:
+                assert s in printed, notprinted_msg.format(s, self.channel, printed)
         return False
 
 printed_msg = """Found {0!r} in printed output (on {1}):
@@ -387,7 +392,10 b' class AssertNotPrints(AssertPrints):'
         setattr(sys, self.channel, self.orig_stream)
         printed = self.buffer.getvalue()
         for s in self.s:
-            assert s not in printed, printed_msg.format(s, self.channel, printed)
+            if isinstance(s, _re_type):
+                assert not s.search(printed), printed_msg.format(s.pattern, self.channel, printed)
+            else:
+                assert s not in printed, printed_msg.format(s, self.channel, printed)
         return False
 
 @contextmanager