# in examples/json-c/repo:
../configure    # use the custom c2rust configure script
intercept-build make
make check
python3 ../translate.py
ninja -C rust

This will produce rust/libjson-c.so.4.0.0.

# in examples/json-c/repo:

# Replace the C libjson-c.so with a symlink to the Rust one.
# You only need to do this the first time.
rm .libs/libjson-c.so.4.0.0
ln -s ../rust/libjson-c.so.4.0.0 .libs/libjson-c.so.4.0.0

# Run tests
make check

If you modify the C files, make check will try to rebuild some stuff and then will break because of the object files that translate.py deleted. If this happens, run make clean && make, then repeat the "running tests" steps from the top.