Currently Argument Clinic converters are tested by running Argument Clinic on the CPython source tree. If it generates incorrect code, then it contains bugs. But not all combinations of standard converters and options are used in the stdlib.

The programming interface of Argument Clinic is complex, and it is hard to write tests for testing only specific functionality. The simplest way of testing Argument Clinic is to write a C file containing declarations and generated code for all test cases. Although this does not allow to test error cases.

The proposed PR adds Lib/test/clinic_test.c which contains tests for all standard converters. It will be extended in bpo-20180 (PR #9828) and bpo-23867.