Testing obsolete interfaces

[Aaron Bentley]

Jan Hudec wrote:
> Hello,
> 
> The test suite prints all deprecation warnings on the error output. But isn't
> it supposed to test deprecated interfaces as long as they are kept around?

Whenever an interface becomes deprecated, none of the core code should
use it.  Printing deprecation warnings during test runs is a good way to
catch that when it does happen.

It's hard to distinguish between tests of deprecated functions and tests
of undeprecated functions that happen to call deprecated functions,
which means we're getting error output even for deprecations warnings we
expect.

Perhaps we need a decorator to suppress expected deprecations warnings
for test cases that exercise deprecated interfaces.

Aaron