Crate protest_insta 

Property-Based Snapshot Testing with Insta

This crate provides integration between Protest property-based testing and Insta snapshot testing.

Overview

Property-based snapshot testing allows you to:

• Test with diverse, generated inputs while keeping visual regression testing
• Detect unexpected changes in serialization output
• Document behavior through automatically captured snapshots
• Review changes using Insta’s review workflow

Quick Start

use protest::{Generator, primitives::IntGenerator, config::GeneratorConfig};
use protest_insta::PropertySnapshots;
use serde::Serialize;
use rand::SeedableRng;
use rand::rngs::StdRng;

#[derive(Serialize)]
struct Point { x: i32, y: i32 }

#[test]
fn test_point_serialization() {
    let mut rng = StdRng::seed_from_u64(42);
    let config = GeneratorConfig::default();
    let generator = IntGenerator::new(0, 100);

    let mut snapshots = PropertySnapshots::new("point_serialization");

    for _ in 0..5 {
        let x = generator.generate(&mut rng, &config);
        let y = generator.generate(&mut rng, &config);
        let point = Point { x, y };
        snapshots.assert_json_snapshot(&point);
    }
}

Features

• Generator Integration: Use any Protest generator for snapshot inputs
• Automatic Naming: Sequential snapshot names for property-based tests
• JSON Support: Built-in JSON serialization for snapshots
• Debug Support: Snapshot any Debug type
• Insta Workflow: Full compatibility with Insta’s review tools

Examples

JSON Snapshot Testing

use protest::{Generator, primitives::VecGenerator, primitives::IntGenerator};
use protest::{config::GeneratorConfig};
use protest_insta::PropertySnapshots;
use serde::Serialize;
use rand::SeedableRng;
use rand::rngs::StdRng;

#[derive(Serialize)]
struct Data {
    values: Vec<i32>,
    sum: i32,
}

#[test]
fn test_data_processing() {
    let mut rng = StdRng::seed_from_u64(123);
    let config = GeneratorConfig::default();
    let generator = VecGenerator::new(IntGenerator::new(0, 10), 1, 5);

    let mut snapshots = PropertySnapshots::new("data_processing");

    for _ in 0..3 {
        let values = generator.generate(&mut rng, &config);
        let sum: i32 = values.iter().sum();
        let data = Data { values, sum };
        snapshots.assert_json_snapshot(&data);
    }
}

Debug Snapshot Testing

use protest::{Generator, primitives::IntGenerator, config::GeneratorConfig};
use protest_insta::PropertySnapshots;
use rand::SeedableRng;
use rand::rngs::StdRng;

#[test]
fn test_computation_output() {
    let mut rng = StdRng::seed_from_u64(456);
    let config = GeneratorConfig::default();
    let generator = IntGenerator::new(1, 100);

    let mut snapshots = PropertySnapshots::new("computation");

    for _ in 0..5 {
        let n = generator.generate(&mut rng, &config);
        let result = (1..=n).sum::<i32>();
        snapshots.assert_debug_snapshot(&result);
    }
}

Structs

PropertySnapshots

Helper for managing property-based snapshots

Functions

property_snapshot_test

Helper function to run a property-based test with snapshot assertions