The page is in working progress, beware!
It's a huge test suite which contains at least 45000 test cases (c/c++ template generated code). The zip file size is 86 MB but the unzipped content weights more than 400 MB. So beware of that. Inside the zip file there are two folders: testcases (which contains the real test cases) and testcasesupport (with headers which define some common code used by the majority of the test cases).
Inside testcases there are 116 different folders which contains some of the weaknesses in the CWE list.
The utility of this test suite is that it's possible to check the strength of static code analyser in terms of displayed false positives and false negatives.
In fact, inside each file there are fundamentally two macros:
OMITGOOD: if defined, the available functions to the preprocessor are all bad functions which shows the weakness of the code;
OMITBAD: if defined, the available functions include good code which fixes the weakness of the code.