Unit Test F.I.R.S.T Principle is ALL you NEED

Writing unit tests might sound like a boring task, but it’s what separates a professional developer from someone who’s just playing with code.

Unit tests are small, automated tests that check if a specific part of your program (called a "unit") works as expected.

But not all tests are created equal.

The faster and more reliable your unit tests are, the easier your life becomes as a developer. That’s where the FIRST principles come in.

Let me walk you through this step by step:

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⚡ F - Fast

Fast tests are a must. If your tests take minutes to run, you’ll avoid running them—and that’s where the trouble begins.

Picture this:

• ?‍♂️ Tests that run in seconds? You’ll run them constantly.
• ? Tests that take minutes? Maybe once or twice a day.
• ? Tests that take hours? Forget it—you’ll stop running them altogether.

The solution? Write simple, focused tests that don’t rely on the internet, databases, or large file systems.

A clean unit test should run so fast that you barely notice it happening.

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? I - Isolated

Each test should focus on one specific thing.

A test that relies on external factors like a slow network or shared data is asking for trouble. Why? Because it can fail for reasons unrelated to the code you’re testing.

Make sure each test:

• ? Stands on its own.
• ? Has one clear purpose.
• ⛓️‍? Fails for a single reason, making debugging easy.

Isolation keeps your tests clean, predictable, and manageable.

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? R - Repeatable

A good unit test always gives the same result, no matter how many times you run it.

If a test works sometimes but fails other times, it’s unreliable. This can happen because of:

• ? Static data not being reset.
• ?️ Dependence on external systems like APIs.
• ❌ Incorrect use of threads or processes.

To fix this, write tests that are fully controlled by your code—nothing external. This makes your tests repeatable and trustworthy.

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✅ S - Self-Verifying

A unit test should clearly pass or fail. No guessing.

If you have to manually check logs or interpret the results, your test isn’t self-verifying. A good test is like a green light or a red light—no gray areas.

When your tests are self-verifying, you can trust the results and move forward confidently.

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⏳ T - Timely

Write your tests before you write your code.

This is known as Test-Driven Development (TDD) and it forces you to think about what your code should do before you build it.

Tests written later (Test-After Development, or TAD) are often incomplete, hard to write, and less useful.

Writing tests first makes your code:

• ? Easier to understand.
• ? Designed with clarity in mind.
• ? Free from unnecessary complexity.

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? Congratulations. With the FIRST principles, you can write tests that are fast, reliable, and genuinely helpful.

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Thank you for your time. Make sure to leave a comment if you have any questions.

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