vyndr/tests/unit/servedGrade.test.js

'use strict';

/**
 * The letter a user sees.
 *
 * What these protect: that no input manufactures an A, that a band which cannot
 * be distinguished from the base rate SAYS so, and that nothing ever renders
 * blank.
 */

const sg = require('../../src/services/model/servedGrade');

describe('no manufactured A — structurally, not by rarity', () => {
  it('no p_win produces an A, A- or A+', () => {
    // The realized rate plateaus around 0.65-0.68 above p_win 0.70, so no band
    // of this forecast has earned a top letter. This is the ceiling made real.
    for (let p = 0; p <= 1.0001; p += 0.01) {
      const g = sg.gradeFor({ p_win: p });
      expect(sg.UNISSUABLE).not.toContain(g.letter);
    }
    expect(sg.BANDS.some((b) => sg.UNISSUABLE.includes(b.letter))).toBe(false);
  });

  it('even a 0.99 forecast tops out at the strongest honest band', () => {
    const g = sg.gradeFor({ p_win: 0.99 });
    expect(g.letter).toBe('B+');
    expect(g.band_realized_rate).toBeLessThan(0.70);
    expect(g.meaning).toMatch(/strongest read/);
  });
});

describe('a band that cannot separate SAYS so', () => {
  it('mid bands are flagged as not distinguishable from base rate', () => {
    for (const p of [0.50, 0.58, 0.66]) {
      const g = sg.gradeFor({ p_win: p });
      expect(g.separates_from_base_rate).toBe(false);
      // The copy must not imply a separation the band does not have.
      expect(g.meaning).toMatch(/base rate|base-rate/);
    }
  });

  it('the extremes do separate, and are marked so', () => {
    expect(sg.gradeFor({ p_win: 0.85 }).separates_from_base_rate).toBe(true);
    expect(sg.gradeFor({ p_win: 0.20 }).separates_from_base_rate).toBe(true);
  });

  it('every band carries its own realized rate, not a target', () => {
    for (const b of sg.BANDS) {
      expect(b.realized).toBeGreaterThan(0);
      expect(b.realized).toBeLessThan(0.70);   // the honest ceiling
    }
  });
});

describe('never blank', () => {
  it('a refusal renders a real state with a reason', () => {
    const g = sg.gradeFor({ refused: true, refusal_reason: 'insufficient_data' });
    expect(g.letter).toBeNull();
    expect(g.state).toBe('refused');
    expect(g.label).toBe('NO READ');
    expect(g.meaning).toMatch(/not enough history/);
  });

  it('a juiced-out side says the book ate the edge', () => {
    expect(sg.gradeFor({ refused: true, refusal_reason: 'juiced_no_edge' }).meaning).toMatch(/vig/);
  });

  it('a missing forecast renders, rather than returning nothing', () => {
    const g = sg.gradeFor({ p_win: null });
    expect(g.state).toBe('no_forecast');
    expect(g.label).toBe('NO READ');
  });

  it('an empty prop still renders', () => {
    expect(sg.gradeFor({}).label).toBe('NO READ');
    expect(sg.gradeFor().label).toBe('NO READ');
  });
});

describe('the basis is stated, never implied', () => {
  it('names when matchup factors moved the forecast', () => {
    const g = sg.gradeFor({ p_win: 0.72, factor_adjustment: { applied: [{ factor: 'platoon_severity' }] } });
    expect(g.basis).toBe('forecast_plus_matchup_factors');
    expect(g.factors_applied).toEqual(['platoon_severity']);
  });

  it('says forecast-only when nothing fired', () => {
    const g = sg.gradeFor({ p_win: 0.72 });
    expect(g.basis).toBe('forecast_only');
    expect(g.factors_applied).toEqual([]);
  });

  it('never claims calibration — the deployed set is empty', () => {
    expect(sg.gradeFor({ p_win: 0.72 }).calibrated).toBe(false);
  });

  it('is monotone: a higher forecast never grades lower', () => {
    const order = ['F', 'D', 'C-', 'C', 'C+', 'B', 'B+'];
    let prev = -1;
    for (let p = 0.02; p <= 0.98; p += 0.02) {
      const i = order.indexOf(sg.gradeFor({ p_win: p }).letter);
      expect(i).toBeGreaterThanOrEqual(prev);
      prev = i;
    }
  });
});