xUnit is a XP style unit testing framework. xUnit uses a protocol between a front-end to display test results and a test driver linked into applications - removing the link time dependencies between the application and the graphics, formatting libraries.
lib4d_sql is a C library providing the required functions (connect, prepare, execute, ...) to write a SQL client for 4D databases. It uses the public 4D SQL protocol wich is supported by 4D products since... the version 11. It is already used by the PDO_