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tests/synapse/engine.test.js (1)

352-361: ⚡ Quick win

Add an explicit layers_errored === 0 assertion for the graceful-degradation path.

The three new error-recording tests (lines 399–442) verify the "null + error" paths well. However, the complementary graceful-degradation path — _safeProcess returns null while getLastError() returns null or is absent — has no assertion on layers_errored. The existing "should return empty xml when no results" test (lines 352–361) covers this setup but only asserts on result.xml; it won't catch a regression where null returns are incorrectly classified as errors in metrics.

Given that this PR's core goal is accurate per-layer error telemetry, a false positive in layers_errored would be a direct regression in the new feature.

✅ Suggested assertion addition to the existing test

   test('should return empty xml when no results', async () => {
     // Make all layers return null
     for (const layer of engine.layers) {
       layer._safeProcess = jest.fn(() => null);
     }

     formatter.formatSynapseRules.mockReturnValue('');
     const result = await engine.process('test', {});
     expect(result.xml).toBe('');
+    // Graceful null returns (no getLastError / getLastError returns null) must NOT
+    // be classified as errors — they are silent skips, not telemetry-visible failures.
+    expect(result.metrics.layers_errored).toBe(0);
   });

Also applies to: 399-442

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@tests/synapse/engine.test.js` around lines 352 - 361, Add an explicit
assertion that no layers were counted as errored when all layers return null:
after calling engine.process in the "should return empty xml when no results"
test, assert that result.metrics.layers_errored === 0 (or the equivalent metrics
field on the returned result). Also add the same assertion to the complementary
graceful-degradation tests that cover the "null + no getLastError()/null" paths
so regressions that treat null returns as errors are caught; locate these tests
by the use of layer._safeProcess mocks and formatter.formatSynapseRules
expectations.