Normally we test integral constant expressions in the Clang test
suite using theint array[foo ? 1 : -1];
idiom. See for example the test/Sema/expr-comma.c test case.
Please note that test/Sema/expr-comma-c89.c contains a test for C99, whilst
test/Sema/expr-comma.c contains a test for C89.
Cheers,
Anton.