Function classify_red_added 

pub fn classify_red_added(
    with: (&CheckResult, Option<&RunnerSummary>),
    without: (&CheckResult, Option<&RunnerSummary>),
) -> RedClass

Classifies a red run against the same command run without the file under test: red by an assertion only where the file adds a failing test — one that did not fail without it (by id when both runs name their tests, else by more failures). A failure the command shows anyway is another test’s, never this file’s red: it is RedClass::Passed.