E2E & Performance Testing

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What does the testing pyramid suggest about test distribution?

javascript

E2E Tests (5-10%)
       /\
      /  \
     /    \
    / Integ\
   /  Tests\
  / (15-30%)\
 /___________\
  Unit Tests
   (60-80%)

AMany unit tests (base), fewer integration tests (middle), fewer end-to-end tests (top).

BWrite equal numbers of unit, integration, and end-to-end tests.

CMost tests should be end-to-end tests.

DTesting pyramid is outdated.

What is snapshot testing?

javascript

// First run: Snapshot is created
test("should render user profile", () => {
  const profile = renderUserProfile({ name: "Alice", age: 30 });
  expect(profile).toMatchSnapshot();
  // Snapshot created with current output
});

// Snapshot file (created automatically)
// __snapshots__/user.test.js.snap
/*
exports[`should render user profile 1`] = `
<div>
  <h1>Alice</h1>
  <p>Age: 30</p>
</div>
`;
*/

// Future runs: Compare against snapshot
// If output changes, test fails and shows diff

ATaking a screenshot of the UI.

BA backup of your test files.

CTesting only image files.

DCapturing the output of a function and comparing future outputs to it.

What tools can you use to debug JavaScript performance issues?

javascript

performance.mark("start");
// Code to measure
performance.mark("end");
performance.measure("duration", "start", "end");

const measure = performance.getEntriesByName("duration")[0];
console.log(`Duration: ${measure.duration}ms`);

AConsole.log is enough.

BPerformance issues cannot be debugged.

CPerformance API, Lighthouse, DevTools profiler, WebPageTest.

DOnly browser extensions.

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