09_rapid

Rapid

Rapid is an advanced property-based and model-based testing library for Go. It supports stateful testing and can verify complex state machines and sequences of operations.

📦 Installation

go get pgregory.net/rapid

🎯 Features

• Property-Based Testing: Like Gopter, generates random inputs
• Model-Based Testing: Test stateful systems with state machines
• Shrinking: Minimizes failing test cases
• State Machines: Model system states and transitions
• Assertions: Built-in assertion helpers
• Reproducible: Tests can be replayed with specific seeds

📖 Usage

Basic Property Test

func TestProperty(t *testing.T) {
    rapid.Check(t, func(t *rapid.T) {
        a := rapid.Int().Draw(t, "a")
        b := rapid.Int().Draw(t, "b")
        
        if a + b != b + a {
            t.Fatalf("commutativity failed")
        }
    })
}

Stateful Testing

rapid.Check(t, func(t *rapid.T) {
    stack := []int{}
    
    for i := 0; i < 100; i++ {
        if rapid.Bool().Draw(t, "push?") {
            stack = append(stack, rapid.Int().Draw(t, "val"))
        } else if len(stack) > 0 {
            stack = stack[:len(stack)-1]
        }
    }
})

🚀 Running Tests

go test
go test -v  # See generated values and shrinking
go test -rapid.checks=1000  # More iterations

✅ Pros

• ✅ Powerful stateful testing
• ✅ Excellent shrinking algorithm
• ✅ Model complex state transitions
• ✅ Good for finding race conditions
• ✅ Reproducible test runs

❌ Cons

• ❌ Steep learning curve
• ❌ Complex setup for stateful tests
• ❌ Not suitable for simple unit tests
• ❌ Requires deep system understanding

🔗 Resources

• GitHub Repository
• Documentation

💡 Best Practices

1. Start simple: Begin with property tests before stateful
2. Model carefully: Accurate state models are crucial
3. Use labels: Name drawn values for better debugging
4. Test invariants: Verify properties hold at every state
5. Limit iterations: Balance thoroughness with speed