Unit Testing:
* Scope: Tests individual components (units) of code in isolation. A "unit" is typically a single function, method, or class.
* Goal: Verify that each unit functions correctly on its own, independent of other parts of the system.
* Implementation: Often involves mocking or stubbing dependencies to isolate the unit being tested. This prevents external factors from affecting the test results.
* Example: Testing a function that calculates the area of a circle. The test would only focus on the correctness of the area calculation formula within that function, without considering how the function might be used within a larger program.
Integration Testing:
* Scope: Tests the interaction between multiple units or modules of code. It verifies that different parts of the system work together correctly.
* Goal: Ensure that integrated components work as expected and communicate effectively with each other.
* Implementation: Involves testing the interaction between various units, often using real implementations rather than mocks or stubs.
* Example: Testing that a user interface (UI) component correctly sends data to a database component, and that the database component correctly stores and retrieves the data. This involves testing the interaction between the UI, the code that handles data transmission, and the database access layer.
Here's an analogy:
Imagine building a car.
* Unit testing would be like testing individual parts: the engine, the brakes, the steering wheel, etc., in isolation to make sure each works perfectly on its own.
* Integration testing would be like testing how these parts work together: Does the engine work with the transmission? Does the steering wheel control the wheels correctly? Does the braking system stop the car effectively?
In short: Unit testing focuses on the individual building blocks, while integration testing focuses on how those blocks fit together. Both are crucial for building robust and reliable software. Often, a project will employ both strategies.