Testing of communication libraries for parallel computing plays an important role in parallel computing systems. In general, testing of communication libraries is done by some testers designed to test every or several parts of the libraries separately. However, many errors of libraries can not be tested by the separate methods, and they will appear when many parts of libraries are running by combination of them in term of a kind of complicated and organic way. But it is rather difficult that the complicated and organic combinations result from the design of library testers themselves. This paper proposes two new testing approaches, which are based on the feature of layered library architectures and test lower libraries by portable testers of upper libraries. The testers of upper libraries can also be regarded as application programs of lower libraries, but they are different from general application programs of lower libraries. They almost cover every part of lower libraries, combine them organically, and form a complicated situation in run time, which can not be easily obtained only by testers of lower libraries. In this case, the errors may be exposed which can escape from the testers of lower libraries.