test: add generator freshness contract module (#337)

tests/generator-freshness-contract.test.cjs

@@ -0,0 +1,29 @@
+const { test, describe } = require('node:test');
+const assert = require('node:assert/strict');
+
+const {
+  GENERATOR_FRESHNESS_REASON,
+  evaluateGeneratorFreshness,
+} = require('../scripts/generator-freshness-contract.cjs');
+
+describe('generator freshness contract module', () => {
+  test('fresh when source and generated match exactly', () => {
+    const out = evaluateGeneratorFreshness({ source: 'abc', generated: 'abc' });
+    assert.deepStrictEqual(out, { ok: true, reason: GENERATOR_FRESHNESS_REASON.FRESH });
+  });
+
+  test('stale when source and generated differ', () => {
+    const out = evaluateGeneratorFreshness({ source: 'abc', generated: 'abd' });
+    assert.deepStrictEqual(out, { ok: false, reason: GENERATOR_FRESHNESS_REASON.STALE });
+  });
+
+  test('missing_source when source omitted', () => {
+    const out = evaluateGeneratorFreshness({ generated: 'abc' });
+    assert.deepStrictEqual(out, { ok: false, reason: GENERATOR_FRESHNESS_REASON.MISSING_SOURCE });
+  });
+
+  test('missing_generated when generated omitted', () => {
+    const out = evaluateGeneratorFreshness({ source: 'abc' });
+    assert.deepStrictEqual(out, { ok: false, reason: GENERATOR_FRESHNESS_REASON.MISSING_GENERATED });
+  });
+});