test: cover auto engine behavior

tests/engine.test.ts

@@ -0,0 +1,22 @@
+import { describe, expect, it } from 'vitest';
+import { resolveEngineMode, shouldUseSweetistics } from '../src/lib/engine.js';
+
+describe('engine', () => {
+  it('normalizes engine values and defaults to auto', () => {
+    expect(resolveEngineMode()).toBe('auto');
+    expect(resolveEngineMode('graphql')).toBe('graphql');
+    expect(resolveEngineMode('sweetistics')).toBe('sweetistics');
+    expect(resolveEngineMode('AUTO')).toBe('auto');
+    expect(resolveEngineMode('nope')).toBe('auto');
+  });
+
+  it('uses GraphQL as primary in auto mode', () => {
+    expect(shouldUseSweetistics('auto', false)).toBe(false);
+    expect(shouldUseSweetistics('auto', true)).toBe(false);
+  });
+
+  it('forces engine selection when explicitly set', () => {
+    expect(shouldUseSweetistics('sweetistics', false)).toBe(true);
+    expect(shouldUseSweetistics('graphql', true)).toBe(false);
+  });
+});