budget-app/scripts/bus-factor.test.mjs

import { describe, it, expect } from 'vitest';
import { parseGitLog, computeOwnership, scoreFiles, repoStats } from './bus-factor.mjs';

// --- parseGitLog ---

describe('parseGitLog', () => {
  it('parses a single commit with one file', () => {
    const raw = `commit abc123
Author: Alice <alice@example.com>
Date:   Mon Jan 1 00:00:00 2024

    Initial commit

5\t2\tserver/src/index.js
`;
    const result = parseGitLog(raw);
    expect(result['server/src/index.js']).toEqual({ Alice: 1 });
  });

  it('accumulates multiple commits by the same author', () => {
    const raw = `commit aaa
Author: Alice <alice@example.com>
Date:   Mon Jan 1 00:00:00 2024

    First

3\t0\tserver/src/app.js

commit bbb
Author: Alice <alice@example.com>
Date:   Tue Jan 2 00:00:00 2024

    Second

1\t1\tserver/src/app.js
`;
    const result = parseGitLog(raw);
    expect(result['server/src/app.js']['Alice']).toBe(2);
  });

  it('tracks multiple authors for the same file', () => {
    const raw = `commit aaa
Author: Alice <alice@example.com>
Date:   Mon Jan 1 00:00:00 2024

    Alice commit

2\t0\tclient/src/App.jsx

commit bbb
Author: Bob <bob@example.com>
Date:   Tue Jan 2 00:00:00 2024

    Bob commit

1\t0\tclient/src/App.jsx
`;
    const result = parseGitLog(raw);
    expect(result['client/src/App.jsx']['Alice']).toBe(1);
    expect(result['client/src/App.jsx']['Bob']).toBe(1);
  });

  it('handles multiple files per commit', () => {
    const raw = `commit aaa
Author: Alice <alice@example.com>
Date:   Mon Jan 1 00:00:00 2024

    Multi-file commit

2\t0\tserver/src/a.js
3\t1\tserver/src/b.js
`;
    const result = parseGitLog(raw);
    expect(result['server/src/a.js']['Alice']).toBe(1);
    expect(result['server/src/b.js']['Alice']).toBe(1);
  });

  it('handles rename syntax (old => new)', () => {
    const raw = `commit aaa
Author: Alice <alice@example.com>
Date:   Mon Jan 1 00:00:00 2024

    Rename

2\t0\told/path.js => new/path.js
`;
    const result = parseGitLog(raw);
    expect(result['new/path.js']).toBeDefined();
    expect(result['old/path.js']).toBeUndefined();
  });

  it('returns empty object for empty log', () => {
    expect(parseGitLog('')).toEqual({});
  });
});

// --- computeOwnership ---

describe('computeOwnership', () => {
  it('computes bus-factor of 1 for a solo author', () => {
    const result = computeOwnership({ Alice: 10 });
    expect(result.busFactor).toBe(1);
    expect(result.totalCommits).toBe(10);
    expect(result.primaryOwner.name).toBe('Alice');
    expect(result.primaryOwner.pct).toBe(1);
  });

  it('computes bus-factor of 2 when two authors each own >= 10%', () => {
    const result = computeOwnership({ Alice: 8, Bob: 2 });
    expect(result.busFactor).toBe(2);
  });

  it('does not count authors below the threshold', () => {
    // Bob has 5% — below default 10% threshold
    const result = computeOwnership({ Alice: 19, Bob: 1 });
    expect(result.busFactor).toBe(1);
  });

  it('respects a custom ownership threshold', () => {
    // With 20% threshold, Bob (10%) doesn't count
    const result = computeOwnership({ Alice: 9, Bob: 1 }, 0.2);
    expect(result.busFactor).toBe(1);
  });

  it('sorts authors by commit count descending', () => {
    const result = computeOwnership({ Alice: 3, Bob: 7, Carol: 5 });
    expect(result.authors[0].name).toBe('Bob');
    expect(result.authors[1].name).toBe('Carol');
    expect(result.authors[2].name).toBe('Alice');
  });

  it('handles empty author counts gracefully', () => {
    const result = computeOwnership({});
    expect(result.totalCommits).toBe(0);
    expect(result.busFactor).toBe(0);
    expect(result.primaryOwner).toBeNull();
  });
});

// --- scoreFiles ---

describe('scoreFiles', () => {
  const ownership = {
    'server/src/risk.js': { Alice: 9, Bob: 1 },       // bus-factor 1 (Bob < 10%)
    'server/src/shared.js': { Alice: 5, Bob: 5 },      // bus-factor 2
    'server/src/tiny.js': { Alice: 1 },                // below minCommits=2, filtered
  };

  it('filters files below minCommits', () => {
    const results = scoreFiles(ownership, { minCommits: 2 });
    expect(results.find(f => f.file === 'server/src/tiny.js')).toBeUndefined();
  });

  it('includes files at or above minCommits', () => {
    const results = scoreFiles(ownership, { minCommits: 2 });
    const files = results.map(f => f.file);
    expect(files).toContain('server/src/risk.js');
    expect(files).toContain('server/src/shared.js');
  });

  it('sorts lowest bus-factor first', () => {
    const results = scoreFiles(ownership, { minCommits: 2 });
    expect(results[0].file).toBe('server/src/risk.js');
    expect(results[1].file).toBe('server/src/shared.js');
  });

  it('returns empty array for empty ownership', () => {
    expect(scoreFiles({}, {})).toEqual([]);
  });
});

// --- repoStats ---

describe('repoStats', () => {
  it('returns zeros for empty input', () => {
    const stats = repoStats([]);
    expect(stats.avgBusFactor).toBe(0);
    expect(stats.highRiskCount).toBe(0);
    expect(stats.totalFiles).toBe(0);
  });

  it('counts high-risk files (busFactor === 1)', () => {
    const files = [
      { busFactor: 1, totalCommits: 10, authors: [] },
      { busFactor: 2, totalCommits: 5, authors: [] },
      { busFactor: 1, totalCommits: 3, authors: [] },
    ];
    const stats = repoStats(files);
    expect(stats.highRiskCount).toBe(2);
    expect(stats.totalFiles).toBe(3);
  });

  it('computes weighted average bus-factor', () => {
    const files = [
      { busFactor: 1, totalCommits: 10, authors: [] },
      { busFactor: 3, totalCommits: 10, authors: [] },
    ];
    const stats = repoStats(files);
    // (1*10 + 3*10) / 20 = 2
    expect(stats.avgBusFactor).toBe(2);
  });
});