These benchmarks require Core_bench which is not a dependency of Yojson,
because it is not part of the regular installation/testing flow. This is solely
meant for developers that are worried about performance changes in Yojson.
This is also why it is deemed appropriate to depend on a benchmarking library with this many dependencies: we rather spend time writing benchmarks than to build a benchmarking library if a perfectly good one already exists in OCaml.
opam install core_benchmark
make bench in the top level directory.