I went through http://hg.ecmascript.org/tests/test262/file/034836894a85/test/suite/ietestcenter/chapter15/15.3/15.3.4/18.104.22.168 and noticed that a bunch of things are not tested.
For inspiration, John-David Dalton has some tests here: https://twitter.com/#!/jdalton/status/103332156687925249
One of the goal being to test how a user-provided Function.prototype.bind function can emulate the spec expectations.
A couple of attempts can be found on the web:
In order to help improving these shims, it would be good to have tests testing other aspects of Function.prototype.bind. In particular, things that can't be emulated like the fact that a bound function doesn't have a "prototype" property (instanceof works anyway thanks to step 14).
Also, calling [[Construct]] of a bound function should be not different from calling [[Target]].[[Construct]], etc.