SRCmail/lib/ai/retrieval/__tests__/fusion.test.ts

import { describe, expect, it } from 'vitest';
import { reciprocalRankFusion } from '../fusion';
import type { SourceRef } from '../types';

function ref(itemId: string): SourceRef {
  return { product: 'mail', accountId: 'acct-1', collectionId: 'inbox', itemId, chunkIx: 0 };
}

describe('reciprocalRankFusion', () => {
  it('ranks an item found by both legs above one found by only one', () => {
    const local = [{ ref: ref('a'), score: 1 }, { ref: ref('b'), score: 0.9 }];
    const server = [{ ref: ref('a'), score: 0.8 }, { ref: ref('c'), score: 0.7 }];

    const fused = reciprocalRankFusion([local, server], 10);

    expect(fused[0].ref.itemId).toBe('a'); // rank 1 in both legs
    expect(fused.map((f) => f.ref.itemId)).toEqual(['a', 'b', 'c']);
  });

  it('degrades to a single retriever when one leg is empty, no special-casing needed', () => {
    const local = [{ ref: ref('a'), score: 1 }, { ref: ref('b'), score: 0.5 }];
    const fused = reciprocalRankFusion([local, []], 10);
    expect(fused.map((f) => f.ref.itemId)).toEqual(['a', 'b']);
  });

  it('returns nothing when both legs are empty', () => {
    expect(reciprocalRankFusion([[], []], 10)).toEqual([]);
  });

  it('respects the limit', () => {
    const local = [ref('a'), ref('b'), ref('c')].map((r, i) => ({ ref: r, score: 1 - i * 0.1 }));
    const fused = reciprocalRankFusion([local, []], 2);
    expect(fused).toHaveLength(2);
  });

  it('does not double-count the same item across legs when collectionId differs', () => {
    // Same email, but the two legs report a different mailbox for it - see
    // fusion.ts's refKey comment for why collectionId is deliberately not
    // part of the fusion identity.
    const local = [{ ref: { ...ref('a'), collectionId: 'inbox' }, score: 1 }];
    const server = [{ ref: { ...ref('a'), collectionId: 'archive' }, score: 1 }];
    const fused = reciprocalRankFusion([local, server], 10);
    expect(fused).toHaveLength(1);
  });
});