vitest

Unit Testing

Vitest allows you to write and run unit tests for your JavaScript/TypeScript code. The example shows a simple test suite for a math operation.

import { describe, it, expect } from 'vitest';
describe('math', () => {
  it('should add numbers correctly', () => {
    expect(1 + 1).toBe(2);
  });
});

Mocking

Vitest provides a built-in mocking utility, allowing you to create mock functions and spy on their behavior.

import { vi } from 'vitest';
const mockFunction = vi.fn(() => 42);
mockFunction();
expect(mockFunction).toHaveBeenCalled();

Snapshot Testing

Vitest supports snapshot testing, which is useful for ensuring your UI does not change unexpectedly. It saves the 'snapshot' of the output and compares it against future test runs.

import { expect, test } from 'vitest';
test('snapshot test', () => {
  const user = { id: 1, name: 'John Doe' };
  expect(user).toMatchSnapshot();
});

Code Coverage

Vitest can generate code coverage reports to help you understand which parts of your codebase are covered by tests.

// Run Vitest with the --coverage flag to generate code coverage reports
// vitest run --coverage

Watch Mode

Vitest's watch mode re-runs tests when it detects changes in the test files or the corresponding source files, providing instant feedback during development.

// Run Vitest in watch mode using the --watch flag
// vitest --watch