Скачать или смотреть Unit Testing & TDD Explained: Red-Green-Refactor, Mocks

Boost your coding skills and interview performance with this complete guide to Unit Testing and Test-Driven Development (TDD)! This video is designed for learners and interview candidates seeking to understand the foundations, benefits, patterns, and best practices behind reliable software testing.

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What Is Unit Testing?
Unit testing is the process of validating isolated pieces of your application's code—a "unit" usually being a single function or class—to ensure it behaves correctly under different scenarios.

Goal: Catch bugs early and guarantee code reliability, maintainability, and flexibility.

AAA Pattern:

Arrange: Set up the test scenario (objects, data, dependencies).

Act: Execute the target function/method.

Assert: Confirm that the actual output matches expected results.

Example:
A Calculator's add() method can be unit tested with simple cases (2 + 3 = 5). More complex cases may use stubs or mocks to replace dependencies (e.g., database connectors) for isolated testing.

Mocking and Stubbing in Unit Tests
Stub: A basic, hardcoded fake for a dependency (returns fixed data).

Mock: A more advanced substitute, used to check specific method calls and arguments, ensuring code interacts as expected.

What Is Test-Driven Development (TDD)?
TDD flips the standard software workflow:

Write a failing test first (Red)

Implement the minimal code to make the test pass (Green)

Refactor the code and tests for clarity and efficiency (Refactor)

Benefits of TDD:

High Test Coverage: Every feature is backed by robust tests.

Better Design: Encourages low coupling and clear interfaces.

Safety Net: Refactor fearlessly—tests will catch regressions!

Living Documentation: Tests serve as executable specs for your code’s behavior.

Real-World Impact and Interview Context
TDD is widely adopted by agile teams and top tech companies.

Unit testing and TDD often appear in interview coding rounds, take-home assignments, and design interviews.

Today’s best engineers use unit tests as a first line of defense for scalable, maintainable code.

Keywords for Ranking
unit testing, TDD, test-driven development, AAA pattern, mocks, stubs, red-green-refactor, software testing, interview preparation, code quality, agile, design patterns, test automation, backend testing, continuous integration, coding interviews, maintainable code

Timestamps
0:00 – Introduction to Unit Testing
2:15 – The AAA Pattern Explained
5:30 – Code Example: Calculator Unit Test
8:40 – Stubs vs Mocks in Testing
12:20 – What is TDD?
14:20 – The Red-Green-Refactor Cycle
17:35 – Benefits of TDD
20:45 – Real-World Impact
23:00 – Interview Tips & Sample Questions

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