snapshot-testing

1# Snapshot Testing with Verify
2 
3## When to Use This Skill
4 
5Use snapshot testing when:
6- Verifying rendered output (HTML emails, reports, generated code)
7- Approving public API surfaces for breaking change detection
8- Testing HTTP response bodies and headers
9- Validating serialization output
10- Catching unintended changes in complex objects
11 
12---
13 
14## What is Snapshot Testing?
15 
16Snapshot testing captures output and compares it against a human-approved baseline:
17 
181. **First run**: Test generates a `.received.` file with actual output
192. **Human review**: Developer approves it, creating a `.verified.` file
203. **Subsequent runs**: Test compares output against `.verified.` file
214. **Changes detected**: Test fails, diff tool shows differences for review
22 
23This catches **unintended changes** while allowing **intentional changes** through explicit approval.
24 
25---
26 
27## Installation
28 
29### Add Verify Package
30 
31```bash
32dotnet add package Verify.Xunit
33# or for other test frameworks:
34dotnet add package Verify.NUnit
35dotnet add package Verify.MSTest
36```
37 
38### Configure ModuleInitializer
39 
40Create a `ModuleInitializer.cs` in your test project:
41 
42```csharp
43using System.Runtime.CompilerServices;
44 
45public static class ModuleInitializer
46{
47    [ModuleInitializer]
48    public static void Init()
49    {
50        // Use source-file-relative paths for verified files
51        VerifyBase.UseProjectRelativeDirectory("Snapshots");
52 
53        // Configure diff tool (optional - auto-detected)
54…