How to run and debug tests in Jest? What are the common command line options? - 面试题

Jest provides multiple methods for running and debugging tests:

Running Tests:

bash
# Run all tests
jest

# Run specific file
jest path/to/test.spec.js

# Run tests matching pattern
jest --testNamePattern="should add"

# Watch mode (auto-run on file changes)
jest --watch

# Run only failed tests
jest --onlyFailures

# Run tests related to changed files
jest --onlyChanged

Debugging Tests:

1. Using console.log:

javascript
test('debug example', () => {
  const result = calculate(2, 3);
  console.log('Result:', result);
  expect(result).toBe(5);
});

2. Using --verbose option:

bash
jest --verbose

3. Using --no-coverage to disable coverage:

bash
jest --no-coverage

4. Setting breakpoints in tests:

javascript
test('debug with debugger', () => {
  debugger; // Set breakpoint in browser or IDE
  const result = calculate(2, 3);
  expect(result).toBe(5);
});

5. Using Jest debug mode:

bash
# Node.js debugging
node --inspect-brk node_modules/.bin/jest --runInBand

# VSCode debug configuration
{
  "type": "node",
  "request": "launch",
  "name": "Jest Current File",
  "program": "${workspaceFolder}/node_modules/.bin/jest",
  "args": ["${fileBasenameNoExtension}", "--runInBand"],
  "console": "integratedTerminal",
  "internalConsoleOptions": "neverOpen"
}

Common Options:

--runInBand: Run tests sequentially (for debugging)
--detectOpenHandles: Detect unclosed handles
--forceExit: Force exit
--bail: Stop after first test failure