[MERGE] Support old API properly

[John Arbash Meinel]

Aaron Bentley wrote:
> John Arbash Meinel wrote:
>>> When testing deprecated APIs, the way I test them is to have them not
>>> directly import warnings.warn or symbol_versioning.warn. Instead to
>>> import symbol_versioning.
>>>
>>> After that, there is the helper function:
>>> symbol_versioning.set_warning_method()
>>>
>>> This lets you override the default warning method with a collector. And
>>> then you have the opportunity to both assert that the deprecation is
>>> being emitted *and* that it does the right thing.
> 
> Thanks for the tip.  I didn't realize we had that.
> 
> I believe this method is generally useful, so I have automated it as
> assertDeprecated (similar to assertRaises).
> 
> Aaron

+    def assertDeprecated(self, expected, callable, *args, **kwargs):
+        """Assert that a callable is deprecated in a particular way.
+
+        :param expected: a list of the deprecation warnings expected,
in order
+        :param callable: The callable to call
+        :param args: The positional arguments for the callable
+        :param kwargs: The keyword arguments for the callable
+        """
+        local_warnings = []
+        def capture_warnings(msg, cls, stacklevel=None):
+            self.assertEqual(cls, DeprecationWarning)
+            local_warnings.append(msg)
+        method = symbol_versioning.warn
+        symbol_versioning.set_warning_method(capture_warnings)
+        try:
+            callable(*args, **kwargs)
+        finally:
+            result = symbol_versioning.set_warning_method(method)
+        self.assertEqual(expected, local_warnings)
+        return result
+

^- I think assertDeprecated should return the callable's result, not the
result from symbol_versioning.

       try:
           result = callable(*args, **kwargs)
       finally:
           symbol_versioning.set_warning_method(method)
       self.assertEqual(expected, local_warnings)
       return result

That way, we can call something, and have it return something.

Otherwise +1 from me after you write a couple of selftest cases for Robert.

John
=:->


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