fix(cli): Identify and fix a test deadlock (#23411)

If a worker tried to flush large amounts of data right as the test was
ending, it could cause the flush sync marker to get lost.

3 files changed, 23 insertions, 0 deletions

diff --git a/tests/specs/test/worker_large_output/__test__.jsonc b/tests/specs/test/worker_large_output/__test__.jsonc
new file mode 100644
index 000000000..9e6533e8c
--- /dev/null
+++ b/tests/specs/test/worker_large_output/__test__.jsonc
@@ -0,0 +1,4 @@
+{
+  "args": "test main.js",
+  "output": "main.out"
+}
diff --git a/tests/specs/test/worker_large_output/main.js b/tests/specs/test/worker_large_output/main.js
new file mode 100644
index 000000000..0941e60f3
--- /dev/null
+++ b/tests/specs/test/worker_large_output/main.js
@@ -0,0 +1,15 @@
+// Regression test for workers that post large amounts of output as a test is ending. This
+// test should not deadlock, though the output is undefined.
+Deno.test(async function workerOutput() {
+  console.log("Booting worker");
+  const code =
+    "self.postMessage(0); console.log(`hello from worker\n`.repeat(60000));";
+  const worker = new Worker(URL.createObjectURL(new Blob([code])), {
+    type: "module",
+  });
+  await new Promise((r) =>
+    worker.addEventListener("message", () => {
+      r();
+    })
+  );
+});
diff --git a/tests/specs/test/worker_large_output/main.out b/tests/specs/test/worker_large_output/main.out
new file mode 100644
index 000000000..ed130e0fe
--- /dev/null
+++ b/tests/specs/test/worker_large_output/main.out
@@ -0,0 +1,4 @@
+[WILDCARD]
+
+ok | 1 passed | 0 failed ([WILDCARD])
+