diff --git a/src/agents/openai-ws-stream.test.ts b/src/agents/openai-ws-stream.test.ts
index b90caff3e74..91d59977392 100644
--- a/src/agents/openai-ws-stream.test.ts
+++ b/src/agents/openai-ws-stream.test.ts
@@ -29,6 +29,16 @@ import type { InputItem, ResponseCreateEvent } from "./openai-ws-types.js";
 import { log } from "./pi-embedded-runner/logger.js";
 import { SYSTEM_PROMPT_CACHE_BOUNDARY } from "./system-prompt-cache-boundary.js";
 
+function countMatching<T>(items: readonly T[], predicate: (item: T) => boolean) {
+  let count = 0;
+  for (const item of items) {
+    if (predicate(item)) {
+      count += 1;
+    }
+  }
+  return count;
+}
+
 // ─────────────────────────────────────────────────────────────────────────────
 // Mock OpenAIWebSocketManager
 // ─────────────────────────────────────────────────────────────────────────────
@@ -2751,7 +2761,7 @@ describe("createOpenAIWebSocketStreamFn", () => {
 
     expect(streamSimpleCalls.length).toBeGreaterThanOrEqual(1);
     expect(manager.closeCallCount).toBeGreaterThanOrEqual(1);
-    expect(events.filter((event) => event.type === "start")).toHaveLength(1);
+    expect(countMatching(events, (event) => event.type === "start")).toBe(1);
     expect(events.some((event) => event.type === "error")).toBe(false);
     const doneEvent = events.find((event) => event.type === "done");
     expect(doneEvent?.message?.content?.[0]?.text).toBe("http fallback response");
@@ -2785,7 +2795,7 @@ describe("createOpenAIWebSocketStreamFn", () => {
 
     expect(streamSimpleCalls.length).toBeGreaterThanOrEqual(1);
     expect(manager.closeCallCount).toBeGreaterThanOrEqual(1);
-    expect(events.filter((event) => event.type === "start")).toHaveLength(1);
+    expect(countMatching(events, (event) => event.type === "start")).toBe(1);
     expect(events.some((event) => event.type === "error")).toBe(false);
     const doneEvent = events.find((event) => event.type === "done");
     expect(doneEvent?.message?.content?.[0]?.text).toBe("http fallback response");
@@ -2820,7 +2830,7 @@ describe("createOpenAIWebSocketStreamFn", () => {
 
     expect(streamSimpleCalls).toHaveLength(0);
     expect(firstManager.closeCallCount).toBeGreaterThanOrEqual(1);
-    expect(events.filter((event) => event.type === "start")).toHaveLength(1);
+    expect(countMatching(events, (event) => event.type === "start")).toBe(1);
     const doneEvent = events.find((event) => event.type === "done");
     expect(doneEvent?.message?.content?.[0]?.text).toBe("retry succeeded");
   });
diff --git a/src/logging/diagnostic.test.ts b/src/logging/diagnostic.test.ts
index 8fbf42f4c7d..a3f29555935 100644
--- a/src/logging/diagnostic.test.ts
+++ b/src/logging/diagnostic.test.ts
@@ -52,6 +52,16 @@ function flushDiagnosticEvents() {
   return new Promise<void>((resolve) => setImmediate(resolve));
 }
 
+function countMatching<T>(items: readonly T[], predicate: (item: T) => boolean) {
+  let count = 0;
+  for (const item of items) {
+    if (predicate(item)) {
+      count += 1;
+    }
+  }
+  return count;
+}
+
 describe("diagnostic session state pruning", () => {
   beforeEach(() => {
     vi.useFakeTimers();
@@ -691,7 +701,7 @@ describe("stuck session diagnostics threshold", () => {
       markDiagnosticEmbeddedRunStarted({ sessionId: "s1", sessionKey: "main" });
       vi.advanceTimersByTime(16_000);
 
-      expect(events.filter((event) => event.type === "session.long_running")).toHaveLength(1);
+      expect(countMatching(events, (event) => event.type === "session.long_running")).toBe(1);
 
       vi.advanceTimersByTime(28_000);
       emitDiagnosticEvent({
@@ -702,7 +712,7 @@ describe("stuck session diagnostics threshold", () => {
       });
       vi.advanceTimersByTime(2_000);
 
-      expect(events.filter((event) => event.type === "session.long_running")).toHaveLength(1);
+      expect(countMatching(events, (event) => event.type === "session.long_running")).toBe(1);
     } finally {
       unsubscribe();
     }
@@ -1038,14 +1048,14 @@ describe("stuck session diagnostics threshold", () => {
 
       vi.advanceTimersByTime(30_000);
       vi.advanceTimersByTime(90_000);
-      expect(events.filter((event) => event === "diagnostic.liveness.warning")).toHaveLength(1);
+      expect(countMatching(events, (event) => event === "diagnostic.liveness.warning")).toBe(1);
 
       vi.advanceTimersByTime(30_000);
     } finally {
       unsubscribe();
     }
 
-    expect(events.filter((event) => event === "diagnostic.liveness.warning")).toHaveLength(2);
+    expect(countMatching(events, (event) => event === "diagnostic.liveness.warning")).toBe(2);
   });
 
   it("does not start the heartbeat when diagnostics are disabled by config", () => {