school_compare/nextjs-app/__tests__/lib/compareChartData.test.ts

/**
 * buildCompareChart: every selected school must produce a rendered series
 * (regression guard for the production bug where a third school's line
 * vanished), the x-axis must include cancelled/unpublished years as real
 * gaps (never compressing time), and the England overlay renders dashed
 * with no gap-bridging.
 */

import { buildCompareChart, fillAcademicYears } from '@/lib/compareChartData';
import type { ComparisonData } from '@/lib/types';

function school(urn: number, years: Array<[number, number | null]>): ComparisonData {
  return {
    school_info: { urn, school_name: `School ${urn}` } as ComparisonData['school_info'],
    yearly_data: years.map(([year, v]) => ({ year, rwm_expected_pct: v })) as ComparisonData['yearly_data'],
  };
}

const THREE_SCHOOLS = {
  '1': school(1, [[201819, 87], [202223, 87], [202425, 87]]),
  '2': school(2, [[201819, 88], [202223, 88], [202425, 92]]),
  '3': school(3, [[201819, 69], [202223, 62], [202425, 79]]),
};

const SCHOOL_LIST = [1, 2, 3].map((urn) => ({ urn, school_name: `School ${urn}` }));

describe('fillAcademicYears', () => {
  it('fills every academic year between min and max', () => {
    expect(fillAcademicYears([201819, 202223])).toEqual([
      201819, 201920, 202021, 202122, 202223,
    ]);
  });
});

describe('buildCompareChart', () => {
  it('renders one series per selected school — none silently dropped', () => {
    const chart = buildCompareChart(THREE_SCHOOLS, SCHOOL_LIST, 'rwm_expected_pct');
    expect(chart.schoolDatasets).toHaveLength(3);
    for (const ds of chart.schoolDatasets) {
      expect(ds.data.some((v) => v != null)).toBe(true);
    }
  });

  it('ignores a no-results school whose only row has a null year', () => {
    // A school with no performance rows comes back from /api/compare with a
    // single phantom yearly_data row (LEFT JOIN) where year and every metric
    // are null. That null year must NOT pollute the axis: Math.trunc(null) is
    // 0, and filling from year 0 blows past the real years, blanking every
    // school's line. Regression guard for "add a no-data school → chart empty".
    const withNoData = {
      ...THREE_SCHOOLS,
      '4': school(4, [[null as unknown as number, null]]),
    };
    const list = [...SCHOOL_LIST, { urn: 4, school_name: 'School 4' }];
    const chart = buildCompareChart(withNoData, list, 'rwm_expected_pct');

    // The real years still drive the axis; the phantom year 0 is gone.
    expect(chart.years).toContain(201819);
    expect(chart.years).toContain(202425);
    expect(chart.years).not.toContain(0);
    // The three real schools still render their lines.
    for (const urn of [1, 2, 3]) {
      const ds = chart.schoolDatasets[urn - 1];
      expect(ds.data.some((v) => v != null)).toBe(true);
    }
  });

  it('handles float years from the API (202425.0 style)', () => {
    const floaty = {
      '1': school(1, [[201819.0 as number, 80], [202425.0 as number, 85]]),
    };
    const chart = buildCompareChart(floaty, [SCHOOL_LIST[0]], 'rwm_expected_pct');
    expect(chart.schoolDatasets[0].data.filter((v) => v != null)).toHaveLength(2);
  });

  it('includes cancelled/unpublished years as null gaps, not compressed time', () => {
    const chart = buildCompareChart(THREE_SCHOOLS, SCHOOL_LIST, 'rwm_expected_pct');
    expect(chart.years).toContain(201920);
    expect(chart.years).toContain(202122);
    const idx = chart.years.indexOf(202021);
    expect(chart.schoolDatasets[0].data[idx]).toBeNull();
  });

  it('adds a dashed England overlay when national data is supplied', () => {
    const chart = buildCompareChart(THREE_SCHOOLS, SCHOOL_LIST, 'rwm_expected_pct', {
      201819: 64.9,
      202122: 58.7,
      202223: 59.5,
      202425: 62.1,
    });
    expect(chart.englandDataset).not.toBeNull();
    const eng = chart.englandDataset!;
    expect(eng.label).toBe('England average');
    expect(eng.borderDash).toEqual([5, 4]);
    expect(eng.spanGaps).toBe(false);
    // England has a value for 2021/22 even though schools do not
    expect(eng.data[chart.years.indexOf(202122)]).toBe(58.7);
  });

  it('lists England-only years so the component can caption dashed-only stretches', () => {
    const chart = buildCompareChart(THREE_SCHOOLS, SCHOOL_LIST, 'rwm_expected_pct', {
      202122: 58.7,
    });
    expect(chart.englandOnlyYears).toEqual([202122]);
    const none = buildCompareChart(THREE_SCHOOLS, SCHOOL_LIST, 'rwm_expected_pct');
    expect(none.englandOnlyYears).toEqual([]);
  });

  it('flags the unpublished 2021/22 school-level year when England has data but schools do not', () => {
    const withNational = buildCompareChart(THREE_SCHOOLS, SCHOOL_LIST, 'rwm_expected_pct', {
      202122: 58.7,
    });
    expect(withNational.showUnpublished202122Note).toBe(true);
    const withoutNational = buildCompareChart(THREE_SCHOOLS, SCHOOL_LIST, 'rwm_expected_pct');
    expect(withoutNational.showUnpublished202122Note).toBe(false);
  });
});