vyndr/tests/unit/rankingInstrument.test.js

'use strict';

/**
 * Ranking instrument — challenger vs incumbent (2026-08-01).
 *
 * These lock the reason the challenger exists: measured on n=200 settled MLB
 * rows, corr(p_win, outcome) = +0.26 while corr(edge, outcome) = -0.010 under
 * the incumbent ruler and -0.022 under the consensus ruler. A quantity that
 * does not predict must not rank, gate or decide.
 */

const {
  rankGrades, rankByForecast, rankingDelta, gradeKey, takeablePWin,
} = require('../../src/utils/gradeRanking');

const g = (player, grade, p_win, odds = -110, extra = {}) => ({
  player, stat_type: 'hits', line: 1.5, direction: 'over',
  grade, p_win, book_odds: odds, ...extra,
});

describe('rankByForecast — the challenger', () => {
  it('contains NO edge term: edge cannot move the order at all', () => {
    const a = [g('A', 'B', 0.62, -110, { edge: -99 }), g('B', 'B', 0.55, -110, { edge: +99 })];
    const b = [g('A', 'B', 0.62, -110, { edge: +99 }), g('B', 'B', 0.55, -110, { edge: -99 })];
    expect(rankByForecast(a).map((x) => x.player)).toEqual(['A', 'B']);
    expect(rankByForecast(b).map((x) => x.player)).toEqual(['A', 'B']);
  });

  it('leads with p_win, not the grade letter', () => {
    // The letter measured r ~ 0.005 and is INVERTED; p_win measures +0.26.
    // A high-p_win C must outrank a low-p_win A.
    const out = rankByForecast([g('lowPwinA', 'A', 0.51), g('highPwinC', 'C', 0.74)]);
    expect(out[0].player).toBe('highPwinC');
  });

  it('keeps the takeable gate — raw p_win would crown chalk', () => {
    const chalk = g('chalk', 'A', 0.93, -300);      // untakeable price
    const real = g('real', 'B', 0.61, -115);
    expect(takeablePWin(chalk)).toBeNull();
    expect(rankByForecast([chalk, real])[0].player).toBe('real');
  });

  it('sorts a missing p_win LAST, never first (Number(null) === 0 guard)', () => {
    const out = rankByForecast([g('none', 'A', null), g('has', 'C', 0.58)]);
    expect(out.map((x) => x.player)).toEqual(['has', 'none']);
  });

  it('is stable for genuinely tied rows', () => {
    const rows = [g('first', 'B', 0.6), g('second', 'B', 0.6)];
    expect(rankByForecast(rows).map((x) => x.player)).toEqual(['first', 'second']);
  });

  it('drops ungraded rows, like the incumbent', () => {
    expect(rankByForecast([g('x', null, 0.9), g('y', 'B', 0.5)]).map((r) => r.player)).toEqual(['y']);
  });
});

describe('rankGrades — the incumbent is UNTOUCHED (live ordering byte-identical)', () => {
  it('still leads with the grade letter and still consults edge', () => {
    const out = rankGrades([g('lowPwinA', 'A', 0.51), g('highPwinC', 'C', 0.74)]);
    expect(out[0].player).toBe('lowPwinA');   // grade-first, unchanged
  });

  it('edge still breaks a true tie in the incumbent', () => {
    const out = rankGrades([
      g('lowEdge', 'B', 0.6, -110, { edge: 1 }),
      g('highEdge', 'B', 0.6, -110, { edge: 9 }),
    ]);
    expect(out[0].player).toBe('highEdge');
  });
});

describe('rankingDelta — the challenger-first measurement', () => {
  it('reports how far the board moves and whether the top read changes', () => {
    const rows = [g('A', 'A', 0.52), g('B', 'C', 0.77), g('C', 'B', 0.64)];
    const d = rankingDelta(rows, 3);
    expect(d.n).toBe(3);
    expect(d.incumbent_top).toBe(gradeKey(rows[0]));   // A-grade leads incumbent
    expect(d.challenger_top).toBe(gradeKey(rows[1]));  // highest p_win leads challenger
    expect(d.top_changed).toBe(true);
    expect(d.moved).toBeGreaterThan(0);
  });

  it('reports zero movement when both instruments agree', () => {
    const rows = [g('A', 'A', 0.80), g('B', 'B', 0.60), g('C', 'C', 0.40)];
    const d = rankingDelta(rows, 3);
    expect(d.moved).toBe(0);
    expect(d.top_changed).toBe(false);
    expect(d.top_n_overlap_pct).toBe(100);
  });

  it('changes nothing about the inputs (pure)', () => {
    const rows = [g('A', 'A', 0.52), g('B', 'C', 0.77)];
    const snapshot = JSON.stringify(rows);
    rankingDelta(rows);
    expect(JSON.stringify(rows)).toBe(snapshot);
  });
});