Unit tests

Unit tests only work ondebug builds.

Unit tests are tests that use functions that are libcurl internal andtherefore not part of any public API, headers or external documentation.

If the internal function you want to test is madestatic, they shouldinstead be setUNITTEST - which then makes debug builds not use static forthem and they then become accessible to test from unit tests.

We provide a set of convenience functions and macros for unit tests to make itquick and easy to write them.

All unit test programs are kept intests/unit