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32 lines
653 B
Markdown
32 lines
653 B
Markdown
# Interface Design for Testability
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Good interfaces make testing natural:
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1. **Accept dependencies, don't create them**
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```typescript
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// Testable
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function processOrder(order, paymentGateway) {}
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// Hard to test
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function processOrder(order) {
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const gateway = new StripeGateway();
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}
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```
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2. **Return results, don't produce side effects**
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```typescript
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// Testable
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function calculateDiscount(cart): Discount {}
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// Hard to test
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function applyDiscount(cart): void {
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cart.total -= discount;
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}
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```
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3. **Small surface area**
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- Fewer methods = fewer tests needed
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- Fewer params = simpler test setup
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