CCA Prep
JS-Dev-101UA

Lesson 7.1Lesson 24 of 24

Effective unit tests

With a block of code and the associated Unit Test, determine where the test is ineffective and modify it to make it more effective.

Effective unit testsIneffective testChecks only that the result is truthyDepends on another test or on thetimeAsserts on a stub or a private fieldDoes not await the async assertionEffective testChecks the exact expected valueArranges its own fixed dataStubs only the dependenciesReturns or awaits the promise

Key points

  1. 1A good test fails when the behaviour breaks. Assert the exact expected value, not just that something is truthy or that no error was thrown.
  2. 2Each test sets up its own data. A test that passes only after another test has run is not isolated.
  3. 3Replace the clock, random numbers and network with values you control, so the result is the same on every run.
  4. 4Stub or spy on dependencies, never on the code under test. Assert results and outgoing calls, not private fields.
  5. 5An async test must wait for its assertions: return the promise or await it, including assert.rejects.
What the exam guide checks here

Objective wording from the exam guide (English).

  • 7.1.K1What makes a unit test effective: isolated, deterministic, one behaviour, meaningful assertions
  • 7.1.K2Test doubles: stubs, spies and mocks; testing asynchronous code
  • 7.1.S1Find why a given test passes without proving the behaviour, and fix it

Lock it in

Answer scenario questions on this topic. Every option comes with an explanation.

Practise 7.1 · 12 questions