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Backend Nodejs Testing Tooling Interview Questions

75 verified Backend Nodejs Testing Tooling interview questions — solve with answers, learn from explanations, test yourself in a real simulation.

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Sample questions

Nodejs Testing ToolingDifficulty 1
describe('math', () => {
  it('adds numbers', () => {
    expect(1 + 2).toBe(3);
  });
});

What does it(...) represent in this code?
  • aA group of related tests
  • bA single test case✓
  • cA setup hook run before tests
  • dAn assertion library
Explanation:it() (an alias of test()) defines one individual test case with a description and a callback containing the actual assertions. describe() is what groups related tests together.
Nodejs Testing ToolingDifficulty 1
What is the primary purpose of a describe() block in Jest/Mocha?
  • aTo define an individual test case that makes assertions
  • bTo group related test cases together for organization/reporting✓
  • cTo register a hook that runs after all tests
  • dTo install npm dependencies before running tests
Explanation:describe() creates a logical grouping of related tests, mainly for organization and readable reporting; the actual assertions live inside it()/test() callbacks.
Nodejs Testing ToolingDifficulty 1
test('is truthy', () => {
  expect(true).toBe(true);
  expect(false).toBe(true);
});

What is the result of running this test?
  • aIt passes because the first assertion passes
  • bIt passes because Jest only checks the last assertion
  • cIt fails because two assertions in one test are not allowed
  • dIt fails because the second expect call throws✓
Explanation:A test can contain multiple assertions, but as soon as one expect(...) call fails, it throws, and the whole test is marked as failed. Here expect(false).toBe(true) fails, so the test fails overall.
Nodejs Testing ToolingDifficulty 1
What is beforeEach() used for in a test suite?
  • aRunning setup code once before all tests in a file
  • bSkipping a test conditionally
  • cRunning setup code before every individual test in scope✓
  • dRestoring mocked modules after the test file completes
Explanation:beforeEach() registers a callback that runs before every individual test within its scope, useful for resetting fresh state for each test.
Nodejs Testing ToolingDifficulty 1
{
  "name": "sample-app",
  "scripts": {
    "test": "jest",
    "start": "node index.js"
  }
}

Running npm test in this project executes which command?
  • anode index.js
  • bjest✓
  • cnpm install
  • dNothing, because npm test requires a pretest script
Explanation:npm test runs whatever command is defined under scripts.test in package.json, which here is jest.
Nodejs Testing ToolingDifficulty 1
Why are testing libraries like Jest or Mocha typically listed under devDependencies instead of dependencies in package.json?
  • aBecause they are only needed during development/testing, not in the running production app✓
  • bBecause devDependencies are installed faster than dependencies
  • cBecause npm forbids test tools from being regular dependencies
  • dBecause devDependencies are automatically excluded from package-lock.json
Explanation:devDependencies lists packages needed only for development and testing workflows; they are not required to run the built/production application, which is why test frameworks belong there.

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