Test that the system/global scopes are really cleared

Rather than just not having the configuration variable we add.

- Keep testing the current failure mode where the unusually named
  `never_path` files can actually exist.

- Also test for paths for those scopes' configuration files, coming
  from the environment.

- Test that the output of showing the full scope's contents is
  empty, of all values. Note that this includes the system scope
  but not all scopes higher than the global scope: the "unknown"
  scope associated with an Apple Git configuration is deliberately
  not asserted to be cleared here. (`gix-testtools` possibly
  intentionally does not clear that scope for fixture scripts.)

Author: EliahKagan

tests/tools/src/lib.rs

@@ -885,24 +885,29 @@ mod tests {
         assert_eq!(git_version_from_bytes(b"git version 2.37.2\n").unwrap(), (2, 37, 2));
     }
 
-    fn check_configure_clears_scope(scope_option: &str) {
+    fn check_configure_clears_scope(scope_env_var: &str, scope_option: &str) {
         let temp = tempfile::TempDir::new().expect("can create temp dir");
+
         #[cfg(windows)]
-        let names = ["-"];
+        let names = ["config", "-"];
         #[cfg(not(windows))]
-        let names = ["-", ":"];
+        let names = ["config", "-", ":"];
         for name in names {
-            File::create(temp.path().join(name))
+            File::create_new(temp.path().join(name))
                 .expect("can create file")
                 .write_all(b"[foo]\n\tbar = baz\n")
                 .expect("can write contents");
         }
+
         let mut cmd = std::process::Command::new("git");
-        let args = ["config", scope_option, "foo.bar"].map(String::from);
+        cmd.env(scope_env_var, "config"); // configure_command() should override it.
+        let args = ["config", "-l", "--show-origin", scope_option].map(String::from);
         configure_command(&mut cmd, &args, temp.path());
+
         let output = cmd.output().expect("can run git");
         let stdout = output.stdout.to_str().expect("valid UTF-8");
         let status = output.status.code().expect("terminated normally");
+
         assert_eq!(stdout, "", "should be no config variable to display");
         assert_eq!(status, 1, "exit status should indicate config variable is absent");
 
@@ -911,11 +916,11 @@ mod tests {
 
     #[test]
     fn configure_command_clears_system_scope() {
-        check_configure_clears_scope("--system");
+        check_configure_clears_scope("GIT_CONFIG_SYSTEM", "--system");
     }
 
     #[test]
     fn configure_command_clears_global_scope() {
-        check_configure_clears_scope("--global");
+        check_configure_clears_scope("GIT_CONFIG_GLOBAL", "--global");
     }
 }