Formal and testable API definition

Is there a formal language-independent language for describing an API? I want to define a utility library to be used across a number of architectures and would like some way to programatically test that all API functions have been implemented and, ideally, run some unit tests of the functions across platforms.

For example, I'll be wanting to write a .Net开发者_开发知识库 Assembly in C#, a Windows DLL in C++, a MacOS library in Objective-C, and a Linux shared library in C++.

Thrift:

Thrift is a remote procedure call (RPC) framework developed at Facebook for "scalable cross-language services development". It combines a software stack with a code generation engine to build services that work efficiently and seamlessly between C++, C#, Java, Perl, Python, PHP, Erlang and Ruby. Although developed at Facebook, it is now an open source project in the Apache Software Foundation Incubator. The implementation was described in an April 2007 technical paper released by Facebook, now hosted on Apache.

Here is a good link: Interface description language.