boocode/apps/server/src/services/__tests__/doom-loop.test.ts

import { describe, it, expect } from 'vitest';
import { DOOM_LOOP_THRESHOLD, detectDoomLoop } from '../inference/index.js';
import type { ToolCall } from '../../types/api.js';

// ---- fixture ----------------------------------------------------------------
// Tiny helper. `id` is required on ToolCall but irrelevant to detection —
// detectDoomLoop compares name + JSON.stringify(args). Counter-based id keeps
// each call unique so we don't accidentally test id-based equality.

let counter = 0;
function mkCall(name: string, args: Record<string, unknown> = {}): ToolCall {
  counter += 1;
  return { id: `c${counter}`, name, args };
}

// ---- below-threshold -------------------------------------------------------

describe('detectDoomLoop — below threshold', () => {
  it('returns null for an empty array', () => {
    expect(detectDoomLoop([])).toBeNull();
  });

  it('returns null when fewer than DOOM_LOOP_THRESHOLD calls exist', () => {
    // 2 < 3 — sliding-window can't form even if both match.
    const a = mkCall('view_file', { path: 'a.ts' });
    const b = mkCall('view_file', { path: 'a.ts' });
    expect(detectDoomLoop([a, b])).toBeNull();
  });
});

// ---- positive detection ----------------------------------------------------

describe('detectDoomLoop — positive matches', () => {
  it('returns name + args when exactly DOOM_LOOP_THRESHOLD identical calls land', () => {
    const calls = [
      mkCall('grep', { pattern: 'TODO', path: 'src' }),
      mkCall('grep', { pattern: 'TODO', path: 'src' }),
      mkCall('grep', { pattern: 'TODO', path: 'src' }),
    ];
    const result = detectDoomLoop(calls);
    expect(result).not.toBeNull();
    expect(result!.name).toBe('grep');
    expect(result!.args).toEqual({ pattern: 'TODO', path: 'src' });
  });

  it('matches sliding window — last DOOM_LOOP_THRESHOLD match even with earlier non-matching calls', () => {
    // 4 calls: first differs, last 3 are identical → fire.
    const calls = [
      mkCall('list_dir', { path: '/' }),
      mkCall('view_file', { path: 'a.ts' }),
      mkCall('view_file', { path: 'a.ts' }),
      mkCall('view_file', { path: 'a.ts' }),
    ];
    const result = detectDoomLoop(calls);
    expect(result).not.toBeNull();
    expect(result!.name).toBe('view_file');
  });

  it('matches identical empty-args calls (defense against {} !== {} reference bug)', () => {
    // JSON.stringify on two distinct {} both produce '{}'. Confirms the
    // detector uses value-equality not reference-equality.
    const calls = [mkCall('ping', {}), mkCall('ping', {}), mkCall('ping', {})];
    expect(detectDoomLoop(calls)).not.toBeNull();
  });

  it('matches calls with nested args of equal shape', () => {
    // Deep-equal via JSON.stringify. If the model emits the same nested
    // object three times, that's still a loop.
    const nested = { filter: { glob: '*.ts', case: 'sensitive' }, limit: 50 };
    const calls = [
      mkCall('find_files', { ...nested }),
      mkCall('find_files', { ...nested }),
      mkCall('find_files', { ...nested }),
    ];
    expect(detectDoomLoop(calls)).not.toBeNull();
  });
});

// ---- negative detection ----------------------------------------------------

describe('detectDoomLoop — negative cases', () => {
  it('returns null when 3 calls share name but differ in args', () => {
    const calls = [
      mkCall('view_file', { path: 'a.ts' }),
      mkCall('view_file', { path: 'b.ts' }),
      mkCall('view_file', { path: 'c.ts' }),
    ];
    expect(detectDoomLoop(calls)).toBeNull();
  });

  it('returns null when 3 calls share args but differ in name', () => {
    const calls = [
      mkCall('view_file', { path: 'a.ts' }),
      mkCall('grep', { path: 'a.ts' }),
      mkCall('list_dir', { path: 'a.ts' }),
    ];
    expect(detectDoomLoop(calls)).toBeNull();
  });

  it('returns null when the FIRST three of four match but the latest differs', () => {
    // Critical sliding-window edge: detector must ONLY look at the last
    // DOOM_LOOP_THRESHOLD entries. Earlier matches don't count if the
    // model has since moved on.
    const calls = [
      mkCall('grep', { pattern: 'X' }),
      mkCall('grep', { pattern: 'X' }),
      mkCall('grep', { pattern: 'X' }),
      mkCall('view_file', { path: 'a.ts' }),
    ];
    expect(detectDoomLoop(calls)).toBeNull();
  });

  it('returns null when args have same keys but different values', () => {
    const calls = [
      mkCall('grep', { pattern: 'TODO', path: 'src' }),
      mkCall('grep', { pattern: 'TODO', path: 'src' }),
      mkCall('grep', { pattern: 'TODO', path: 'apps' }),
    ];
    expect(detectDoomLoop(calls)).toBeNull();
  });
});

// ---- threshold contract ----------------------------------------------------

describe('DOOM_LOOP_THRESHOLD', () => {
  it('is a positive integer (the public contract — tests assume 3)', () => {
    expect(DOOM_LOOP_THRESHOLD).toBeGreaterThan(0);
    expect(Number.isInteger(DOOM_LOOP_THRESHOLD)).toBe(true);
  });
});