test: add generic error handler test (500)

Co-authored-by: shenald-dev <245350826+shenald-dev@users.noreply.github.com>

Author: google-labs-jules[bot]

.jules/bolt.md

@@ -20,3 +20,11 @@ The `heavyComputation` function was being called repeatedly with identical argum
 
 Action:
 Implemented a `Map`-based cache for `heavyComputation` in `src/index.js`. Subsequent calls with the same `iterations` parameter now return the cached result in $O(1)$ time (~0.01ms), improving performance by several orders of magnitude for repeated inputs. Added unit tests in `tests/heavy_computation.test.js` to verify correctness and timing improvements.
+
+## 2026-03-20 — Tested Generic Error Handler
+
+Learning:
+The generic error handler in the API was returning a 500 status code but was not covered by any automated tests, leaving a gap in coverage for unexpected server-side failures.
+
+Action:
+Added a test case in `tests/api.test.js` that intentionally mocks a failure in an internal dependency (`crypto.randomUUID`) to trigger the generic error handler. The test asserts that the handler returns a 500 status code and a sanitized JSON response (`{ error: 'Internal server error' }`) without leaking stack traces. Additionally, `console.error` was temporarily suppressed during the test to keep test output clean.

tests/api.test.js

@@ -45,3 +45,31 @@ test('POST /v1/chat/completions fails with invalid JSON gracefully', async () =>
   assert.strictEqual(res.status, 400);
   assert.strictEqual(res.body.error, 'Invalid JSON payload');
 });
+
+test('Generic error handler returns 500 without leaking stack traces', async () => {
+  const crypto = require('crypto');
+  const originalRandomUUID = crypto.randomUUID;
+  const originalConsoleError = console.error;
+
+  // Mock internal failure
+  crypto.randomUUID = () => { throw new Error('Mock internal failure'); };
+
+  // Suppress expected console.error from the error handler
+  console.error = () => {};
+
+  try {
+    const res = await request(app)
+      .post('/v1/chat/completions')
+      .send({
+        model: 'gpt-4',
+        messages: [{ role: 'user', content: 'Hello!' }]
+      });
+
+    assert.strictEqual(res.status, 500);
+    assert.deepStrictEqual(res.body, { error: 'Internal server error' });
+  } finally {
+    // Restore originals
+    crypto.randomUUID = originalRandomUUID;
+    console.error = originalConsoleError;
+  }
+});