Snapshot Testing

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

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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.

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Installation

Add Verify Package

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:

using System.Runtime.CompilerServices;