Port run-make/libtest-junit to rmake

Author: Zalathar

Diff for: src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -9,7 +9,6 @@ run-make/incr-add-rust-src-component/Makefile
 run-make/issue-84395-lto-embed-bitcode/Makefile
 run-make/jobserver-error/Makefile
 run-make/libs-through-symlinks/Makefile
-run-make/libtest-junit/Makefile
 run-make/libtest-thread-limit/Makefile
 run-make/macos-deployment-target/Makefile
 run-make/min-global-align/Makefile

Diff for: tests/run-make/libtest-junit/Makefile

@@ -0,0 +1,31 @@
+// Check libtest's JUnit (XML) output against snapshots.
+
+//@ ignore-cross-compile
+//@ needs-unwind (test file contains #[should_panic] test)
+
+use run_make_support::{cmd, diff, python_command, rustc};
+
+fn main() {
+    rustc().arg("--test").input("f.rs").run();
+
+    run_tests(&[], "output-default.xml");
+    run_tests(&["--show-output"], "output-stdout-success.xml");
+}
+
+#[track_caller]
+fn run_tests(extra_args: &[&str], expected_file: &str) {
+    let cmd_out = cmd("./f")
+        .env("RUST_BACKTRACE", "0")
+        .args(&["-Zunstable-options", "--test-threads=1", "--format=junit"])
+        .args(extra_args)
+        .run_fail();
+    let test_stdout = &cmd_out.stdout_utf8();
+
+    python_command().arg("validate_junit.py").stdin(test_stdout).run();
+
+    diff()
+        .expected_file(expected_file)
+        .actual_text("stdout", test_stdout)
+        .normalize(r#"\btime="[0-9.]+""#, r#"time="$$TIME""#)
+        .run();
+}