Wait for the killed expression worker to exit in the timeout test

On timeout the parent sends SIGKILL to the wrapper's process group and
reaps only the wrapper. The worker spinning in JavaScript exits once the
kernel has delivered the signal and torn the process down, which on a
runner busy with four xdist workers can still be pending when the test
looks: psutil reported it as running. Poll for up to 10 s instead. A
worker that is never killed still fails the test.

test/unit/app/tools/test_expression_basics.py

@@ -26,6 +26,7 @@ from galaxy.tools.expressions.js_engine import (
     resolve_isolation_command,
     SandboxedJSEngine,
 )
+from galaxy.util.wait import wait_on
 from galaxy_ext.expressions.sandbox_worker import MAX_MESSAGE_BYTES
 
 # A benign stand-in for a real jail command (e.g. bwrap): `/usr/bin/env` just execs
@@ -318,12 +319,16 @@ def test_timeout_kills_worker_under_waiting_wrapper(tmp_path, short_timeout_grac
             sandbox_command=[sys.executable, str(wrapper), str(pid_file)],
         )
     pid = int(pid_file.read_text())
-    try:
-        child = psutil.Process(pid)
-        # The orphaned worker is reaped asynchronously by init or a subreaper.
-        assert child.status() in (psutil.STATUS_ZOMBIE, psutil.STATUS_DEAD)
-    except psutil.NoSuchProcess:
-        pass
+
+    def worker_exited():
+        try:
+            # The orphaned worker is reaped asynchronously by init or a subreaper.
+            return psutil.Process(pid).status() in (psutil.STATUS_ZOMBIE, psutil.STATUS_DEAD) or None
+        except psutil.NoSuchProcess:
+            return True
+
+    # SIGKILL takes effect asynchronously; on a busy machine the worker can still run for a moment.
+    wait_on(worker_exited, "killed expression worker to exit", timeout=10, delta=0.05)
 
 
 @_needs_env