title: “Testing NonNull with Miri” meta_description: “Comprehensive testing strategies for NonNull usage including Miri validation.” keywords: [“miri nonnull”, “nonnull testing”, “rust unsafe testing”]

🧪 Reinventing from Scratch: NonNull<T>

Chapter 10 — “Tests, Miri, and Safety Checklist”

“Test with Miri, or test in production.”

✅ 10.1. Basic Tests

#[test]
fn test_nonnull_construction() {
    let x = 42;
    let ptr = NonNull::new(&x as *const i32 as *mut i32);
    assert!(ptr.is_some());
    
    let null = NonNull::<i32>::new(std::ptr::null_mut());
    assert!(null.is_none());
}

#[test]
fn test_niche_optimization() {
    use std::mem::size_of;
    assert_eq!(
        size_of::<Option<NonNull<u8>>>(),
        size_of::<*mut u8>()
    );
}

🔬 10.2. Miri Validation

cargo +nightly miri test

Miri will catch:

• Use-after-free
• Invalid pointer arithmetic
• Alignment violations
• Provenance issues

🧠 10.3. Safety Checklist

When using NonNull:

• Pointer is actually non-null
• Memory is allocated and valid
• Proper alignment for type T
• Have permission to access
• Lifetime doesn’t outlive allocation

Next: Chapter 11 — Appendix: Reference Implementations 📚