diff --git a/denops/@denops-private/cli_test.ts b/denops/@denops-private/cli_test.ts
index 13594e2d..a88b9290 100644
--- a/denops/@denops-private/cli_test.ts
+++ b/denops/@denops-private/cli_test.ts
@@ -288,7 +288,7 @@ Deno.test("main()", async (t) => {
         );
 
         await t.step("and the worker stream is closed", async (t) => {
-          fakeWorker.onmessage(new MessageEvent("message", { data: null }));
+          fakeWorker.onmessage!(new MessageEvent("message", { data: null }));
           await delay(0);
 
           await t.step("calls Worker.terminate()", () => {
@@ -453,7 +453,7 @@ Deno.test("main()", async (t) => {
         assertSpyCalls(globalThis_Worker, 1);
         fakeTcpListener.close();
 
-        fakeWorker.onmessage(new MessageEvent("message", { data: null }));
+        fakeWorker.onmessage!(new MessageEvent("message", { data: null }));
         await delay(0);
 
         await t.step("calls Worker.terminate()", () => {
@@ -557,7 +557,7 @@ Deno.test("main()", async (t) => {
         await delay(0);
 
         await t.step("and the worker stream is closed", async (t) => {
-          fakeWorker.onmessage(new MessageEvent("message", { data: null }));
+          fakeWorker.onmessage!(new MessageEvent("message", { data: null }));
           await delay(0);
 
           await t.step("outputs error logs", () => {
diff --git a/denops/@denops-private/worker_test.ts b/denops/@denops-private/worker_test.ts
index d2009376..9fa0ed96 100644
--- a/denops/@denops-private/worker_test.ts
+++ b/denops/@denops-private/worker_test.ts
@@ -145,8 +145,13 @@ for (const { host, mode } of matrix) {
           throw error;
         });
 
-        await delay(0);
-        assertEquals(consoleStub.error.firstCall.args, [
+        // NOTE: The unhandledrejection event dispatch timing varies across
+        // platforms and Deno versions. Poll until console.error is called.
+        const deadline = Date.now() + 5000;
+        while (!consoleStub.error.firstCall && Date.now() < deadline) {
+          await delay(10);
+        }
+        assertEquals(consoleStub.error.firstCall?.args, [
           "Unhandled rejection:",
           error,
         ]);
diff --git a/tests/denops/testutil/mock_test.ts b/tests/denops/testutil/mock_test.ts
index 6a9af175..b5f5bb33 100644
--- a/tests/denops/testutil/mock_test.ts
+++ b/tests/denops/testutil/mock_test.ts
@@ -24,6 +24,10 @@ type MethodKeyOf<T extends AnyRecord> = ({
   [K in keyof T]: T[K] extends AnyFn ? K : never;
 })[keyof T];
 
+type NullableMethodKeyOf<T extends AnyRecord> = ({
+  [K in keyof T]: T[K] extends AnyFn | null ? K : never;
+})[keyof T];
+
 type GetterKeyOf<T extends AnyRecord> = ({
   [K in keyof T]: T[K] extends AnyFn ? never : K;
 })[keyof T];
@@ -337,7 +341,7 @@ Deno.test("createFakeWorker()", async (t) => {
         "removeEventListener",
         "dispatchEvent",
         "terminate",
-      ] as const satisfies readonly MethodKeyOf<Worker>[];
+      ] as const satisfies readonly NullableMethodKeyOf<Worker>[];
       for (const key of unimplementedMethods) {
         await t.step(`.${key}()`, () => {
           assertThrows(() => (worker[key] as AnyFn)(), Error, "Unimplemented");
diff --git a/tests/denops/testutil/with.ts b/tests/denops/testutil/with.ts
index 7ce1d839..ff0a4713 100644
--- a/tests/denops/testutil/with.ts
+++ b/tests/denops/testutil/with.ts
@@ -56,7 +56,7 @@ export function withVim<T>(
     "-c",
     "visual", // Go to Normal mode
     "-c",
-    "set columns=9999", // Avoid unwilling output newline
+    "set columns=9999 shortmess-=T", // Avoid unwilling output newline/truncation
     ...commands.flatMap((c) => ["-c", c]),
   ];
   return withProcess(cmd, args, { verbose: conf.verbose, ...options });