diff --git a/p/src/commands/run.rs b/p/src/commands/run.rs
index c4296bb..cf584a1 100644
--- a/p/src/commands/run.rs
+++ b/p/src/commands/run.rs
@@ -148,15 +148,8 @@ pub fn execute(worker_name: Option<&str>, cmd: Vec<String>, no_sync: bool) -> Re
 
 /// Build the shell script that runs inside the tmux pane.
 ///
-/// The script:
-///   1. Configures the tmux status bar (job ID, worker, running/done state).
-///   2. Runs the user's command, capturing output to output.log via tee.
-///   3. Writes the exit code to the exitcode file.
-///   4. Updates the status bar to reflect completion.
-///   5. Shows a "press any key to detach" prompt and waits.
-///   6. Calls `tmux detach-client` — the SSH session returns cleanly with no
-///      [exited] or [detached] message flash.
-fn build_run_sh(session: &str, job_dir: &str, work_dir: &str, worker: &str) -> String {
+/// `pub(crate)` so it can be tested.
+pub(crate) fn build_run_sh(session: &str, job_dir: &str, work_dir: &str, worker: &str) -> String {
     // Truncate worker name for display to avoid overflowing the status bar.
     let worker_display = if worker.len() > 20 {
         &worker[..20]
@@ -205,3 +198,75 @@ fn build_run_sh(session: &str, job_dir: &str, work_dir: &str, worker: &str) -> S
         work_dir = work_dir,
     )
 }
+
+// ── Tests ─────────────────────────────────────────────────────────────────────
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn sample_script() -> String {
+        build_run_sh(
+            "p-a3f2b091",
+            "/home/ubuntu/.p/jobs/a3f2b091-0000-0000-0000-000000000000",
+            "/home/ubuntu/.p/workdirs/a3f2b091-0000-0000-0000-000000000000",
+            "beefy",
+        )
+    }
+
+    #[test]
+    fn script_starts_with_shebang() {
+        assert!(sample_script().starts_with("#!/bin/bash\n"));
+    }
+
+    #[test]
+    fn script_contains_session_name() {
+        assert!(sample_script().contains("p-a3f2b091"));
+    }
+
+    #[test]
+    fn script_contains_job_and_work_dirs() {
+        let s = sample_script();
+        assert!(s.contains("/home/ubuntu/.p/jobs/a3f2b091"));
+        assert!(s.contains("/home/ubuntu/.p/workdirs/a3f2b091"));
+    }
+
+    #[test]
+    fn script_captures_exit_code_via_pipestatus() {
+        // Must use PIPESTATUS[0] to get the command's exit code, not tee's.
+        assert!(sample_script().contains("PIPESTATUS[0]"));
+    }
+
+    #[test]
+    fn script_writes_exitcode_file() {
+        assert!(sample_script().contains("exitcode"));
+    }
+
+    #[test]
+    fn script_tees_output_to_log() {
+        assert!(sample_script().contains("tee"));
+        assert!(sample_script().contains("output.log"));
+    }
+
+    #[test]
+    fn script_waits_for_keypress_before_detach() {
+        let s = sample_script();
+        assert!(s.contains("read -rn 1 -s"));
+        assert!(s.contains("tmux detach-client"));
+    }
+
+    #[test]
+    fn script_sets_up_status_bar() {
+        let s = sample_script();
+        assert!(s.contains("status on"));
+        assert!(s.contains("beefy"));
+    }
+
+    #[test]
+    fn worker_name_truncated_at_20_chars() {
+        let s = build_run_sh("p-test", "/j", "/w", "a-very-long-worker-name-here");
+        // "a-very-long-worker-name-here" is 28 chars; only first 20 should appear.
+        assert!(s.contains("a-very-long-worker-n"));
+        assert!(!s.contains("a-very-long-worker-name-here"));
+    }
+}