Function coverage_matrix_with 

pub fn coverage_matrix_with(
    root: &Path,
    analyzer: Option<&str>,
    on_path: impl Fn(&str) -> bool,
) -> Vec<AnalyzerCoverage>

coverage_matrix with the PATH probe supplied by the caller.

The probe is an argument for the reason provisioning takes its fetcher as one: it keeps the decision testable without the ambient state it would otherwise depend on. A test cannot change this process’s PATH — unsafe_code = "forbid" rules out std::env::set_var — so without this seam two of the three Readiness states would be unreachable from a test, on a machine where whether they are reachable at all depends on what happens to be installed.