# Snapshot Testing

Use Verify for snapshot testing in .NET.

- Repository: https://github.com/Aaronontheweb/dotnet-skills (1244 stars)
- Category: Testing
- License: MIT
- Last updated: 2026-10-28
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add Aaronontheweb/dotnet-skills --skill snapshot-testing -g -a claude-code -y`
Codex: `npx skills add Aaronontheweb/dotnet-skills --skill snapshot-testing -g -a codex -y`
Cursor: `npx skills add Aaronontheweb/dotnet-skills --skill snapshot-testing -g -a cursor -y`
Gemini CLI: `npx skills add Aaronontheweb/dotnet-skills --skill snapshot-testing -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add Aaronontheweb/dotnet-skills`

## Description

Use Verify for snapshot testing in .NET. Approve API surfaces, HTTP responses, rendered emails, and serialized outputs. Detect unintended changes through human-reviewed baseline files.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Snapshot Testing with Verify

## When to Use This Skill

Use snapshot testing when:
- Verifying rendered output (HTML emails, reports, generated code)
- Approving public API surfaces for breaking change detection
- Testing HTTP response bodies and headers
- Validating serialization output
- Catching unintended changes in complex objects

---

## What is Snapshot Testing?

Snapshot testing captures output and compares it against a human-approved baseline:

1. **First run**: Test generates a `.received.` file with actual output
2. **Human review**: Developer approves it, creating a `.verified.` file
3. **Subsequent runs**: Test compares output against `.verified.` file
4. **Changes detected**: Test fails, diff tool shows differences for review

This catches **unintended changes** while allowing **intentional changes** through explicit approval.

---

## Installation

### Add Verify Package

```bash
dotnet add package Verify.Xunit
# or for other test frameworks:
dotnet add package Verify.NUnit
dotnet add package Verify.MSTest
```

### Configure ModuleInitializer

Create a `ModuleInitializer.cs` in your test project:

```csharp
using System.Runtime.CompilerServices;

public static class ModuleInitializer
{
    [ModuleInitializer]
    public static void Init()
    {
        // Use source-file-relative paths for verified files
        VerifyBase.UseProjectRelativeDirectory("Snapshots");

        // Configure diff tool (optional - auto-detected)
        // DiffTools.UseOrder(DiffTool.Rider, DiffTool.VisualStudioCode);
    }
}
```

---

## Basic Usage

### Simple Object Verification

```csharp
[Fact]
public Task VerifyUserDto()
{
    var user = new UserDto(
        Id: "user-123",
        Name: "John Doe",
        Email: "john@example.com",
        CreatedAt: new DateTime(2025, 1, 15));

    return Verify(user);
}
```

Creates `VerifyUserDto.verified.txt`:
```json
{
  Id: user-123,
  Name: John Doe,
  Email: john@example.com,
  CreatedAt: 2025-01-15T00:00:00
}
```

The rest: https://github.com/Aaronontheweb/dotnet-skills/blob/HEAD/skills/snapshot-testing/SKILL.md