mod system_prefix {    use super::super::system_prefix_from_exepath_var;    use gix_testtools::tempfile;    use serial_test::serial;    use std::{ffi::OsString, path::PathBuf};     fn if_exepath(key: &str, value: impl Into<OsString>) -> Option<OsString> {        match key {            "EXEPATH" => Some(value.into()),            _ => None,        }    }     struct ExePath {        _tempdir: tempfile::TempDir,        path: PathBuf,    }     impl ExePath {        fn new() -> Self {            let tempdir = tempfile::tempdir().expect("can create new temporary directory");             // This is just `tempdir.path()` unless it is relative, in which case it is resolved.            let path = std::env::current_dir()                .expect("can get current directory")                .join(tempdir.path());             Self {                _tempdir: tempdir,                path,            }        }         fn create_subdir(&self, name: &str) -> PathBuf {            let child = self.path.join(name);            std::fs::create_dir(&child).expect("can create subdirectory");            child        }         fn create_separate_subdirs(&self, names: &[&str]) {            for name in names {                self.create_subdir(name);            }        }         fn create_separate_regular_files(&self, names: &[&str]) {            for name in names {                std::fs::File::create_new(self.path.join(name)).expect("can create new file");            }        }         fn var_os_func(&self, key: &str) -> Option<OsString> {            if_exepath(key, self.path.as_os_str())        }    }     #[test]    fn exepath_unset() {        let outcome = system_prefix_from_exepath_var(|_| None);        assert_eq!(outcome, None);    }     #[test]    fn exepath_no_relevant_subdir() {        for names in [&[][..], &["ucrt64"][..]] {            let exepath = ExePath::new();            exepath.create_separate_subdirs(names);            let outcome = system_prefix_from_exepath_var(|key| exepath.var_os_func(key));            assert_eq!(outcome, None);        }    }     #[test]    fn exepath_unambiguous_subdir() {        for name in ["mingw32", "mingw64", "clangarm64"] {            let exepath = ExePath::new();            let subdir = exepath.create_subdir(name);            let outcome = system_prefix_from_exepath_var(|key| exepath.var_os_func(key));            assert_eq!(outcome, Some(subdir));        }    }     #[test]    fn exepath_unambiguous_subdir_beside_strange_files() {        for (dirname, filename1, filename2) in [            ("mingw32", "mingw64", "clangarm64"),            ("mingw64", "mingw32", "clangarm64"),            ("clangarm64", "mingw32", "mingw64"),        ] {            let exepath = ExePath::new();            let subdir = exepath.create_subdir(dirname);            exepath.create_separate_regular_files(&[filename1, filename2]);            let outcome = system_prefix_from_exepath_var(|key| exepath.var_os_func(key));            assert_eq!(outcome, Some(subdir));        }    }     #[test]    fn exepath_ambiguous_subdir() {        for names in [            &["mingw32", "mingw64"][..],            &["mingw32", "clangarm64"][..],            &["mingw64", "clangarm64"][..],            &["mingw32", "mingw64", "clangarm64"][..],        ] {            let exepath = ExePath::new();            exepath.create_separate_subdirs(names);            let outcome = system_prefix_from_exepath_var(|key| exepath.var_os_func(key));            assert_eq!(outcome, None);        }    }     #[test]    #[serial]    fn exepath_empty_string() {        for name in ["mingw32", "mingw64", "clangarm64"] {            let exepath = ExePath::new();            exepath.create_subdir(name);            let _cwd = gix_testtools::set_current_dir(&exepath.path).expect("can change to test dir");            let outcome = system_prefix_from_exepath_var(|key| if_exepath(key, ""));            assert_eq!(outcome, None);        }    }     #[test]    #[serial]    fn exepath_nonempty_relative() {        for name in ["mingw32", "mingw64", "clangarm64"] {            let grandparent = tempfile::tempdir().expect("can create new temporary directory");            let parent = grandparent                .path()                .canonicalize()                .expect("path to the new directory works")                .join("dir");            std::fs::create_dir_all(parent.join(name)).expect("can create directories");            let _cwd = gix_testtools::set_current_dir(grandparent.path()).expect("can change to test dir");            let outcome = system_prefix_from_exepath_var(|key| if_exepath(key, "dir"));            assert_eq!(outcome, None);        }    }}