6 files changed, 75 insertions, 28 deletions
diff --git a/cli/bench/main.rs b/cli/bench/main.rs
index b98a9d141..e15f76277 100644
--- a/cli/bench/main.rs
+++ b/cli/bench/main.rs
@@ -75,7 +75,7 @@ const EXEC_TIME_BENCHMARKS: &[(&str, &[&str], Option<i32>)] = &[
     &[
       "run",
       "--allow-read",
-      "cli/tests/workers_large_message_bench.ts",
+      "cli/tests/workers/bench_large_message.ts",
     ],
     None,
   ),
diff --git a/cli/tests/workers_large_message_bench.ts b/cli/tests/workers/bench_large_message.ts
index 9cda5a40d..53076e711 100644
--- a/cli/tests/workers_large_message_bench.ts
+++ b/cli/tests/workers/bench_large_message.ts
@@ -1,14 +1,10 @@
 // Copyright 2020 the Deno authors. All rights reserved. MIT license.
 
-// deno-lint-ignore-file
-
-import { deferred } from "../../test_util/std/async/deferred.ts";
-
-function oneWorker(i: any): Promise<void> {
+function oneWorker(i: number) {
   return new Promise<void>((resolve) => {
     let countDown = 10;
     const worker = new Worker(
-      new URL("workers/large_message_worker.js", import.meta.url).href,
+      new URL("worker_large_message.js", import.meta.url).href,
       { type: "module" },
     );
     worker.onmessage = (e): void => {
@@ -23,8 +19,8 @@ function oneWorker(i: any): Promise<void> {
   });
 }
 
-function bench(): Promise<any> {
-  let promises = [];
+function bench() {
+  const promises = [];
   for (let i = 0; i < 50; i++) {
     promises.push(oneWorker(i));
   }
diff --git a/cli/tests/workers/racy_worker.js b/cli/tests/workers/racy_worker.js
index 83756b791..0f66c6278 100644
--- a/cli/tests/workers/racy_worker.js
+++ b/cli/tests/workers/racy_worker.js
@@ -1,21 +1,25 @@
 // See issue for details
 // https://github.com/denoland/deno/issues/4080
 //
-// After first call to `postMessage() this worker schedules
-// [close(), postMessage()] ops on the same turn of microtask queue
-// (because message is rather big).
-// Only single `postMessage()` call should make it
-// to host, ie. after calling `close()` no more code should be run.
+// After first received message, this worker schedules
+// [assert(), close(), assert()] ops on the same turn of microtask queue
+// All tasks after close should not make it
 
-setTimeout(() => {
-  close();
-}, 50);
-
-while (true) {
-  await new Promise((done) => {
+onmessage = async function () {
+  let stage = 0;
+  await new Promise((_) => {
+    setTimeout(() => {
+      if (stage !== 0) throw "Unexpected stage";
+      stage = 1;
+    }, 50);
+    setTimeout(() => {
+      if (stage !== 1) throw "Unexpected stage";
+      stage = 2;
+      postMessage("DONE");
+      close();
+    }, 50);
     setTimeout(() => {
-      postMessage({ buf: new Array(999999) });
-      done();
-    });
+      throw "This should not be run";
+    }, 50);
   });
-}
+};
diff --git a/cli/tests/workers/test.ts b/cli/tests/workers/test.ts
index c3ccebfbb..41988d204 100644
--- a/cli/tests/workers/test.ts
+++ b/cli/tests/workers/test.ts
@@ -198,15 +198,12 @@ Deno.test({
     );
 
     racyWorker.onmessage = (e): void => {
-      assertEquals(e.data.buf.length, 999999);
-      racyWorker.onmessage = (_e): void => {
-        throw new Error("unreachable");
-      };
       setTimeout(() => {
         promise.resolve();
       }, 100);
     };
 
+    racyWorker.postMessage("START");
     await promise;
   },
 });
@@ -726,3 +723,38 @@ Deno.test({
     worker.terminate();
   },
 });
+
+Deno.test({
+  name: "structured cloning postMessage",
+  fn: async function (): Promise<void> {
+    const result = deferred();
+    const worker = new Worker(
+      new URL("worker_structured_cloning.ts", import.meta.url).href,
+      { type: "module" },
+    );
+
+    worker.onmessage = (e): void => {
+      // self field should reference itself (circular ref)
+      const value = e.data.self.self.self;
+
+      // fields a and b refer to the same array
+      assertEquals(value.a, ["a", true, 432]);
+      assertEquals(value.a, ["a", true, 432]);
+      value.b[0] = "b";
+      value.a[2] += 5;
+      assertEquals(value.a, ["b", true, 437]);
+      assertEquals(value.b, ["b", true, 437]);
+
+      const len = value.c.size;
+      value.c.add(1); // This value is already in the set.
+      value.c.add(2);
+      assertEquals(len + 1, value.c.size);
+
+      result.resolve();
+    };
+
+    worker.postMessage("START");
+    await result;
+    worker.terminate();
+  },
+});
diff --git a/cli/tests/workers/large_message_worker.js b/cli/tests/workers/worker_large_message.js
index f7b7da8a0..f7b7da8a0 100644
--- a/cli/tests/workers/large_message_worker.js
+++ b/cli/tests/workers/worker_large_message.js
diff --git a/cli/tests/workers/worker_structured_cloning.ts b/cli/tests/workers/worker_structured_cloning.ts
new file mode 100644
index 000000000..eb1719a9a
--- /dev/null
+++ b/cli/tests/workers/worker_structured_cloning.ts
@@ -0,0 +1,15 @@
+// More info on structured cloning can be found here:
+// https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm
+
+self.onmessage = () => {
+  const arr = ["a", true, 432];
+  const set = new Set([1, 3, 5, 7, 9]);
+  const selfReference = {
+    a: arr,
+    b: arr,
+    c: set,
+  };
+  // deno-lint-ignore no-explicit-any
+  (selfReference as any).self = selfReference;
+  self.postMessage(selfReference);
+};