-code With Mosh- Mastering Javascript Unit Testing -

He wrote his first failing test:

function applyDiscount(user, total) { if (user.type === 'VIP') return total * 0.8; return total; } -Code With Mosh- Mastering JavaScript Unit Testing

"Thirty bucks."

He typed:

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. -Code With Mosh- Mastering JavaScript Unit Testing

And that made him a real engineer.

Mosh drew a diagram. "Don't test the database. Test your logic. Replace the real dependency with a mock." Leo learned to write: -Code With Mosh- Mastering JavaScript Unit Testing