Add testing helpers for mocking and encoding tests.

pandas.util.testing now has a SimpleMock class for mocking objects which
have read-only attributes.
Ths mocking support is used by the *stdin_encoding* context manager to
make it easy to test code with an arbitrary value for sys.stdin.encoding.

pandas/util/testing.py

@@ -7,6 +7,8 @@
 import string
 import sys
 
+from contextlib import contextmanager  # contextlib is available since 2.5
+
 from distutils.version import LooseVersion
 
 from numpy.random import randn
@@ -23,7 +25,6 @@
 from pandas.tseries.period import PeriodIndex
 from pandas.tseries.interval import IntervalIndex
 
-
 Index = index.Index
 Series = series.Series
 DataFrame = frame.DataFrame
@@ -378,3 +379,50 @@ def test_network(self):
 
     t.network = True
     return t
+
+
+class SimpleMock(object):
+    """
+    Poor man's mocking object
+
+    Note: only works for new-style classes, assumes  __getattribute__ exists.
+
+    >>> a = type("Duck",(),{})
+    >>> a.attr1,a.attr2 ="fizz","buzz"
+    >>> b = SimpleMock(a,"attr1","bar")
+    >>> b.attr1 == "bar" and b.attr2 == "buzz"
+    True
+    >>> a.attr1 == "fizz" and a.attr2 == "buzz"
+    True
+    """
+    def __init__(self, obj, *args, **kwds):
+        assert(len(args) % 2 == 0)
+        attrs = kwds.get("attrs", {})
+        attrs.update({k:v for k, v in zip(args[::2], args[1::2])})
+        self.attrs = attrs
+        self.obj = obj
+
+    def __getattribute__(self,name):
+        attrs = object.__getattribute__(self, "attrs")
+        obj = object.__getattribute__(self, "obj")
+        return attrs.get(name, type(obj).__getattribute__(obj,name))
+
+@contextmanager
+def stdin_encoding(encoding=None):
+    """
+    Context manager for running bits of code while emulating an arbitrary
+    stdin encoding.
+
+    >>> import sys
+    >>> _encoding = sys.stdin.encoding
+    >>> with stdin_encoding('AES'): sys.stdin.encoding
+    'AES'
+    >>> sys.stdin.encoding==_encoding
+    True
+
+    """
+    import sys
+    _stdin = sys.stdin
+    sys.stdin = SimpleMock(sys.stdin, "encoding", encoding)
+    yield
+    sys.stdin = _stdin