CAD Test-Driven Development (TDD) 3

Question 1

What is a 'test double' in TDD terminology?

Accepted Answer

A generic term for objects that stand in for real dependencies in tests

Answer

Test doubles (mocks, stubs, fakes, spies, dummies) replace real collaborators to isolate the unit under test.

Question 2

In TDD, what distinguishes a 'stub' from a 'mock'?

Accepted Answer

Stubs return canned responses; mocks verify interactions occurred

Answer

Stubs provide predetermined return values, while mocks additionally assert that specific calls were made.

Question 3

Which metric measures how much of the production code is exercised by tests?

Accepted Answer

Code coverage

Answer

Code coverage reports what percentage of lines, branches, or paths are executed during test runs.

Question 4

A team practicing TDD notices tests are slow and rarely run. The best corrective action is to:

Accepted Answer

Profile and optimize tests, possibly replacing slow I/O with fakes

Answer

Slow tests discourage frequent execution; isolating I/O with fakes or in-memory alternatives restores speed without losing coverage.

Question 5

What does 'Outside-In TDD' (also called London School TDD) emphasize?

Accepted Answer

Starting from the outermost acceptance test and mocking collaborators inward

Answer

Outside-In TDD starts with a failing acceptance test, then drives lower-level units by mocking dependencies not yet built.

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