Test that relative EXEPATH doesn't trigger the optimization

This tests that a nonempty value of `EXEPATH` that is a realtive
path does not trigger the `EXEPATH` optimization of
`system_prefix()` on Windows.

This is similar to the previously introduced test for an empty
value, in that both are treated as relative paths. Like that test,
this one currently fails, but both will pass once the `EXEPATH`
optimization is refined to refuse to look under a non-absolute
path.

Author: EliahKagan

gix-path/src/env/tests.rs

@@ -121,4 +121,21 @@ mod system_prefix {
             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);
+        }
+    }
 }