test: demonstrate the current precedence of finding --jobserver-auth

Author: weihanglo

src/lib.rs

@@ -585,9 +585,9 @@ impl HelperState {
 }
 
 fn find_jobserver_auth(var: &str) -> Option<(&str, usize)> {
-    ["--jobserver-fds=", "--jobserver-auth="]
+    ["--jobserver-auth=", "--jobserver-fds="]
         .iter()
-        .map(|&arg| var.find(arg).map(|pos| (arg, pos)))
+        .map(|&arg| var.rfind(arg).map(|pos| (arg, pos)))
         .find_map(|pos| pos)
 }
 
@@ -597,3 +597,32 @@ fn no_helper_deadlock() {
     let _y = x.clone();
     std::mem::drop(x.into_helper_thread(|_| {}).unwrap());
 }
+
+#[test]
+fn test_find_jobserver_auth() {
+    let cases = [
+        (
+            "--jobserver-auth= --jobserver-auth=",
+            ("--jobserver-auth=", 18),
+        ),
+        (
+            "--jobserver-fds= --jobserver-fds=",
+            ("--jobserver-fds=", 17),
+        ),
+        (
+            "--jobserver-auth= --jobserver-fds= --jobserver-auth=",
+            ("--jobserver-auth=", 35),
+        ),
+        (
+            "--jobserver-fds= --jobserver-auth= --jobserver-fds=",
+            ("--jobserver-auth=", 17),
+        ),
+    ];
+    for (var, expected) in cases {
+        let actual = find_jobserver_auth(var).unwrap();
+        assert_eq!(
+            actual, expected,
+            "expect {expected:?}, got {actual:?}, input `{var:?}`"
+        );
+    }
+}