feat(arr): probe methods for subtitle providers and engines

crates/arr-subs/tests/command.rs

@@ -21,7 +21,7 @@ use std::{
 
 use arr_core::Language;
 use arr_subs::translate::{translate, Error};
-use arr_subs::{Command, CommandConfig};
+use arr_subs::{Backend as _, Command, CommandConfig};
 
 fn cues(texts: &[&str]) -> Vec<arr_subs::Cue> {
     texts
@@ -270,3 +270,25 @@ async fn an_edited_timeout_reaches_the_next_call() {
 }
 
 const DEFAULT: Duration = arr_subs::COMMAND_DEFAULT_TIMEOUT;
+
+/// The lamp (#200) is the command starting and exiting cleanly — not what it
+/// says. An empty batch goes in; only the exit status is judged.
+#[tokio::test]
+async fn a_probe_runs_the_template_and_wants_a_clean_exit() {
+    let dir = tempfile::tempdir().expect("tempdir");
+
+    let ok = stub(dir.path(), "ok.sh", "cat > /dev/null\n");
+    Command::new(config(&ok.display().to_string(), DEFAULT))
+        .expect("backend constructs")
+        .probe()
+        .await
+        .expect("a clean exit is a lit lamp");
+
+    let failing = stub(dir.path(), "fail.sh", "echo nope >&2\nexit 3\n");
+    let error = Command::new(config(&failing.display().to_string(), DEFAULT))
+        .expect("backend constructs")
+        .probe()
+        .await
+        .expect_err("non-zero exit");
+    assert!(matches!(error, Error::Transport { .. }), "got {error:?}");
+}