Mosh drew a diagram. "Don't test the database. Test your logic. Replace the real dependency with a mock." Leo learned to write:
And that made him a real engineer.
Sarah blinked. "How much did that course cost?" -Code With Mosh- Mastering JavaScript Unit Testing
"That’s it," Sarah said, her voice eerily calm. "You’re not writing a single line of new code until you learn how to test the old code."
It felt… clean. The next lesson hit him like a truck. Mosh introduced Test-Driven Development (TDD) . Mosh drew a diagram
Leo turned to Sarah. "I broke the code on purpose. The tests found it in 0.3 seconds."
"Don't test the implementation. Test the behavior. If you're afraid to change your code, your tests are bad." Replace the real dependency with a mock
Last Tuesday was the breaking point. A simple pull request to update a discount function caused a catastrophic cascade. The login failed. The cart emptied. The CEO’s test account showed a total price of . The company had to pay customers to buy things.