i12510.test.diff (for Python 3 only) does the following:
* Turn method CallTips.get_entity into a module function as it does not use the self parameter and is therefore not really an instance method.
* Delete the erroneous _find_constructor function. Even if it were fixed, it is unnecessary at least in 3.x. Class attribute lookup already does the superclass search duplicated in this function and should find object.__init__ if nothing else. (I defaulted to None anyway in case of an unforeseen problem, such as a type subclass that somehow disables the lookup.)
* In get_argspec, remove the lambda stuff that resulted in all classes getting a spurious '()' line. With the fix to retrieving .__init__, it never gets used and is not needed anyway.
* Only delete 'self' from the argument list for classes and bound methods where it is implicit and not to be explicity entered.
* Increase tests from 13 to 37.
* Modernize and re-organize tests with an eye to becoming part of an idlelib test suite.
With the increased number of tests, I am pretty confident in the patch, but I would not mind if you glance at it and try it out on Linux.