pub(crate) fn new(needle_len: usize) -> Runner {
        assert!(needle_len >= 1, "needle_len must be at least 1");
        assert!(needle_len <= 3, "needle_len must be at most 3");
        Runner { needle_len }
    }
Create a new test runner for forward and reverse byte search
implementations.

The `needle_len` given must be at most `3` and at least `1`. It
corresponds to the number of needle bytes to search for.
src/tests/memchr/mod.rs