Handsontable Unit Testing

Module Name Mapping (jest.config.js)

Jest resolves these aliases automatically:

• 'handsontable' and 'handsontable/...' resolve to src/ and src/...
• 'walkontable' and 'walkontable/...' resolve to src/3rdparty/walkontable/src/ and src/3rdparty/walkontable/src/...
• CSS/SCSS imports resolve to test/__mocks__/styleMock.js (returns an empty object).

Pre-configured Mocks

The bootstrap file (test/bootstrap.js) provides these automatically:

• ResizeObserver mock (test/__mocks__/resizeObserverMock.js).
• IntersectionObserver mock (test/__mocks__/intersectionObserverMock.js).

For custom mocking, use jest.fn() for stubs and jest.spyOn(object, 'method') for spying on existing methods.

Run Commands

• All unit tests: npm run test:unit --prefix handsontable
• Targeted: npm run test:unit --testPathPattern=<regex> --prefix handsontable -- the pattern is matched against test file paths (e.g. filters, ghostTable.unit, metaManager)
• Example: npm run test:unit --testPathPattern=filters --prefix handsontable

Important: Do NOT use -- before --testPathPattern. The flag is consumed by npm's script runner, not by Jest directly.

Large Dataset Testing

When the code under test handles data arrays, include tests with 50k+ rows. Use forEach loops to populate arrays -- never arr.push(...largeArray) (causes stack overflow at scale).

Test Structure Example

import { calculateSomething } from '../utils';

describe('calculateSomething', () => {
  it('should return the sum for positive inputs', () => {
    expect(calculateSomething(2, 3)).toBe(5);
  });

  it('should handle zero values', () => {
    expect(calculateSomething(0, 0)).toBe(0);
  });

  it('should throw for invalid input', () => {
    expect(() => calculateSomething(null)).toThrow();
  });
});

Common Mistakes

• Writing unit tests for DOM or rendering behavior (use E2E instead).
• Covering only the happy path -- always test edge cases, error states, and boundary conditions.
• Skipping large dataset tests when the code processes arrays.
• Forgetting to test updateSettings() and enablePlugin()/disablePlugin() cycles for plugin logic.
• Using globals from E2E helpers (handsontable(), selectCell()) -- these are not available in unit tests.

Further Reading

• .ai/TESTING.md for the full testing strategy.
• handsontable/jest.config.js for Jest configuration.
• handsontable/test/__mocks__/ for available mock implementations.
• handsontable/test/bootstrap.js for the test setup.