RedditBot/tests/growth-thread-screening.test.ts

import { describe, expect, it } from 'vitest';
import type { RedditPost } from '../src/reddit/api.js';
import {
  DEFAULT_GROWTH_THREAD_POLICY,
  screenGrowthThread,
} from '../src/services/growth-thread-screening.js';

const NOW = 1_700_000_000_000;

function post(overrides: Partial<RedditPost> = {}): RedditPost {
  return {
    id: 'abc',
    name: 't3_abc',
    subreddit: 'cats',
    author: 'someone',
    title: 'My cat keeps knocking things off shelves',
    url: 'https://www.reddit.com/r/cats/comments/abc/',
    permalink: '/r/cats/comments/abc/',
    thumbnail: '',
    is_self: true,
    // 90 minutes old, comfortably inside the default window.
    created_utc: (NOW - 90 * 60_000) / 1_000,
    over_18: false,
    spoiler: false,
    num_comments: 20,
    ...overrides,
  } as RedditPost;
}

function reason(overrides: Partial<RedditPost>, policy = DEFAULT_GROWTH_THREAD_POLICY): string | null {
  const screening = screenGrowthThread(post(overrides), policy, NOW);
  return screening.eligible ? null : screening.reason;
}

describe('screenGrowthThread', () => {
  it('accepts a thread with traction inside the window', () => {
    expect(screenGrowthThread(post(), DEFAULT_GROWTH_THREAD_POLICY, NOW)).toEqual({ eligible: true });
  });

  describe('threads that cannot accept a comment', () => {
    it.each([
      [{ locked: true }, /locked/],
      [{ archived: true }, /archived/],
      [{ stickied: true }, /stickied/],
      [{ pinned: true }, /stickied/],
      [{ removed_by_category: 'moderator' }, /removed/],
      [{ distinguished: 'moderator' }, /moderator or admin/],
      [{ distinguished: 'admin' }, /moderator or admin/],
      [{ author: '[deleted]' }, /author is deleted/],
      [{ title: '   ' }, /no title/],
    ])('rejects %o', (overrides, expected) => {
      expect(reason(overrides)).toMatch(expected);
    });

    it('allows an ordinary distinguished value through', () => {
      expect(reason({ distinguished: null })).toBeNull();
    });
  });

  describe('age window', () => {
    it('rejects a thread with no traction yet', () => {
      expect(reason({ created_utc: (NOW - 5 * 60_000) / 1_000 })).toMatch(/younger than 15m/);
    });

    it('rejects a thread where a comment would be buried', () => {
      expect(reason({ created_utc: (NOW - 10 * 3_600_000) / 1_000 })).toMatch(/older than 6h/);
    });

    it('rejects a thread dated in the future', () => {
      expect(reason({ created_utc: (NOW + 60_000) / 1_000 })).toMatch(/future/);
    });

    it('accepts the window boundaries', () => {
      expect(reason({ created_utc: (NOW - 15 * 60_000) / 1_000 })).toBeNull();
      expect(reason({ created_utc: (NOW - 6 * 3_600_000) / 1_000 })).toBeNull();
    });
  });

  describe('comment count', () => {
    it('rejects a dead thread', () => {
      expect(reason({ num_comments: 2 })).toMatch(/fewer than 3 comments/);
      expect(reason({ num_comments: undefined })).toMatch(/fewer than 3 comments/);
    });

    it('rejects a thread that is already saturated', () => {
      expect(reason({ num_comments: 400 })).toMatch(/more than 150 comments/);
    });

    it('accepts the count boundaries', () => {
      expect(reason({ num_comments: 3 })).toBeNull();
      expect(reason({ num_comments: 150 })).toBeNull();
    });
  });

  describe('NSFW', () => {
    it('rejects NSFW threads by default', () => {
      expect(reason({ over_18: true })).toMatch(/marked NSFW/);
    });

    it('allows them when the account opts in', () => {
      expect(reason({ over_18: true }, { ...DEFAULT_GROWTH_THREAD_POLICY, allowNsfw: true }))
        .toBeNull();
    });
  });

  it('honours a custom policy', () => {
    const strict = {
      minAgeMs: 60 * 60_000,
      maxAgeMs: 2 * 60 * 60_000,
      minComments: 30,
      maxComments: 50,
      allowNsfw: false,
    };

    expect(reason({ num_comments: 20 }, strict)).toMatch(/fewer than 30/);
    expect(reason({ num_comments: 40 }, strict)).toBeNull();
  });
});