property-based-testing

# Property-Based Testing Expert knowledge for property-based testing - automatically generating test cases to verify code properties rather than testing specific examples. ## Core Expertise **Property-Based Testing Concept** - **Traditional testing**: Test specific examples - **Property-based testing**: Test properties that should hold for all inputs - **Generators**: Automatically create diverse test inputs - **Shrinking**: Minimize failing cases to simplest example - **Coverage**: Explore edge cases humans might miss **When to Use Property-Based Testing** - Mathematical operations (commutative, associative properties) - Encoders/decoders (roundtrip properties) - Parsers and serializers - Data transformations - API contracts - Invariants and constraints ## TypeScript/JavaScript (fast-check) ### Installation ```bash # Using Bun bun add -d fast-check # Using npm npm install -D fast-check ``` ### Basic Example ```typescript import { test } from 'vitest' import * as fc from 'fast-check' // Traditional example-based test test('reverse twice returns original', () => { expect(reverse(reverse([1, 2, 3]))).toEqual([1, 2, 3]) }) // Property-based test test('reverse twice returns original - property based', () => { fc.assert( fc.property( fc.array(fc.integer()), // Generate random arrays of integers (arr) => { expect(reverse(reverse(arr))).toEqual(arr) } ) ) }) // fast-check automatically generates 100s of test cases! ``` ### Built-i...