diff --git a/app/comments.test.js b/app/comments.test.js
index 27927bd..539ac2b 100644
--- a/app/comments.test.js
+++ b/app/comments.test.js
@@ -1,15 +1,22 @@
-import { describe, it } from 'node:test';
+import { describe, it, afterEach } from 'node:test';
 import assert from 'node:assert/strict';
-import fs from 'fs';
-import os from 'os';
-import path from 'path';
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
 import { saveFindings } from './comments.js';
 import { FINDINGS_PATH } from './config.js';
 
 describe('saveFindings', () => {
+  const tempDirs = [];
+  const makeTempDir = prefix => {
+    const dir = fs.mkdtempSync(path.join(os.tmpdir(), prefix));
+    tempDirs.push(dir);
+    return dir;
+  };
+
   it('writes findings to workspace and mirror dirs when provided', () => {
-    const workspace = fs.mkdtempSync(path.join(os.tmpdir(), 'findings-ws-'));
-    const mirrorDir = fs.mkdtempSync(path.join(os.tmpdir(), 'findings-mirror-'));
+    const workspace = makeTempDir('findings-ws-');
+    const mirrorDir = makeTempDir('findings-mirror-');
     const findings = [{ level: 'warning', role: 'Leo', location: 'file.js:1', suggestion: 'test' }];
 
     saveFindings(workspace, findings, mirrorDir);
@@ -19,4 +26,50 @@ describe('saveFindings', () => {
     assert.equal(workspaceText, JSON.stringify(findings, null, 2) + '\n');
     assert.equal(mirrorText, JSON.stringify(findings, null, 2) + '\n');
   });
+
+  it('writes only to workspace when mirrorDir is omitted', () => {
+    const workspace = makeTempDir('findings-ws-');
+    const findings = [{ level: 'info', role: 'Maya', location: 'file.js:2', suggestion: 'note' }];
+
+    saveFindings(workspace, findings);
+
+    const workspaceText = fs.readFileSync(path.join(workspace, FINDINGS_PATH), 'utf8');
+    assert.equal(workspaceText, JSON.stringify(findings, null, 2) + '\n');
+  });
+
+  it('does not duplicate writes when mirrorDir matches workspace', () => {
+    const workspace = makeTempDir('findings-same-');
+    const findings = [];
+    const writeCalls = [];
+    const originalWriteFileSync = fs.writeFileSync;
+
+    fs.writeFileSync = (...args) => {
+      writeCalls.push(args[0]);
+      return originalWriteFileSync(...args);
+    };
+
+    try {
+      saveFindings(workspace, findings, workspace);
+    } finally {
+      fs.writeFileSync = originalWriteFileSync;
+    }
+
+    assert.equal(writeCalls.length, 1);
+    assert.equal(writeCalls[0], path.join(workspace, FINDINGS_PATH));
+  });
+
+  it('writes an empty JSON array when findings is empty', () => {
+    const workspace = makeTempDir('findings-empty-');
+
+    saveFindings(workspace, []);
+
+    const workspaceText = fs.readFileSync(path.join(workspace, FINDINGS_PATH), 'utf8');
+    assert.equal(workspaceText, '[]\n');
+  });
+
+  afterEach(() => {
+    while (tempDirs.length > 0) {
+      fs.rmSync(tempDirs.pop(), { recursive: true, force: true });
+    }
+  });
 });