Verifies small components in isolation.
Unit tests verify small units in isolation with assertions (pytest, JUnit). Good tests are fast, deterministic and independent; use mocks for external dependencies. Coverage metrics show tested lines but not test quality. The test pyramid favours many unit tests, fewer integration and UI tests.
assert add(2,3)==5 is the simplest unit test.
Unit tests catch bugs early and make refactoring safe, which keeps code reliable as it changes.
Verifies small components in isolation.
Unit tests catch bugs early and make refactoring safe, which keeps code reliable as it changes.
It tests one behaviour, is fast and independent, has a clear name and runs without network or external state.
A stand-in object that replaces a real dependency in a test, so the unit can be tested in isolation.
Typical applications include testing a function that converts units to check edge cases, verifying a parser handles empty input correctly and checking that a discount calculation returns the right value at the boundaries.
Study "UML and modelling" first (topic 48 of 104 in Software & Computing). It covers the groundwork this topic builds on.
Arrange-Act-Assert. Test doubles. Edge cases.
assert add(2,3)==5 is the simplest unit test.
The next topic is "Test-driven development", which builds directly on this one.
It is classed as Intermediate in Software & Computing (topic 49 of 104). It is an intermediate topic. Work through the beginner topics in Software & Computing first.
Want to practise? Open the interactive course for quick checks, quizzes, simulations and progress tracking.