Verify Email Snapshots

What the source does

• FilesystemNone observedNo reads or writes in the source
• NetworkNone observedNo outbound calls in the source
• ShellNone observedNo commands run in the source
• DependenciesPinnedNothing floats
• SecretsNone foundNo keys in source

Five audit layers

Gates applied: no behavioural pass.

CLAUDE.md

Audit 0.4.1 · source sha 871f73ffcae3 · 18 Oct 2026Report an issue or request a re-scan

• PublisherAaronontheweb GitHub userOwner of the repository this skill is read from
• Source folderAaronontheweb/dotnet-skills/skills/verify-email-snapshotsThe exact folder we audited
• LicenceMITAs the repository states it
• Commit pinned for this verdict871f73ffcae3A new audit runs when the source changes
• Repository statusNot archivedLast push 7 days ago
• Sandboxed runNot runSkills are read, not executed; layer L4 is skipped

Its description: Snapshot test email templates using Verify to catch regressions. Validates rendered HTML output matches approved baseline. Works with MJML templates and any email renderer.

---
name: verify-email-snapshots
description: Snapshot test email templates using Verify to catch regressions. Validates rendered HTML output matches approved baseline. Works with MJML templates and any email renderer.
user-invocable: false
---

# Snapshot Testing Email Templates with Verify

## When to Use This Skill

Use this skill when:
- Testing email template rendering for regressions
- Validating MJML templates compile to expected HTML
- Reviewing email changes in code review (diffs are visual)
- Ensuring variable substitution works correctly

**Related skills:**
- `aspnetcore/mjml-email-templates` - MJML template authoring
- `aspire/mailpit-integration` - Test email delivery locally
- `testing/snapshot-testing` - General Verify patterns

---

## Why Snapshot Test Emails?

Email templates are:
1. **Visual** - Small changes can break rendering across clients
2. **Hard to unit test** - Output is complex HTML, not simple values
3. **Prone to regression** - Template changes can have unintended effects

Snapshot testing captures the rendered HTML and fails when it changes unexpectedly.

---

## Installation

```bash
dotnet add package Verify.Xunit  # or Verify.NUnit, Verify.MSTest
```

---

## Basic Email Snapshot Test

```csharp
[Fact]
public async Task UserSignupInvitation_RendersCorrectly()
{
    // Arrange
    var renderer = _services.GetRequiredService<IMjmlTemplateRenderer>();

    var variables = new Dictionary<string, string>
    {
        { "PreviewText", "You've been invited to join Acme Corp" },
        { "OrganizationName", "Acme Corporation" },
        { "InviteeName", "John Doe" },
        { "InviterName", "Jane Admin" },
        { "InvitationLink", "https://example.com/invite/abc123" },
        { "ExpirationDate", "December 31, 2025" }
    };

    // Act
    var html = await renderer.RenderTemplateAsync(
        "UserInvitations/UserSignupInvitation",
        variables);

    // Assert
    await Verify(html, extension: "html");
}
```

This creates `UserSignupInvitation_RendersCorrectly.verified.html` on first run.

---

## Reviewing Email Changes

When a template changes, the test fails with a diff. Review options:

### 1. Visual Diff Tool

```bash
# Configure diff tool (one-time)
dotnet tool install -g verify.tool
verify accept  # Accept all pending changes
verify review  # Open diff tool
```

### 2. Browser Preview

Open the `.received.html` file in a browser to see the actual rendering.

### 3. IDE Integration

Most IDEs show inline diffs for `.verified.html` vs `.received.html` files.

---

## Test Each Template Variant

Create tests for each email template to catch regressions:

```csharp
public class EmailTemplateSnapshotTests : IClassFixture<EmailTestFixture>
{
    private readonly IMjmlTemplateRenderer _renderer;

    public EmailTemplateSnapshotTests(EmailTestFixture fixture)
    {
        _renderer = fixture.Services.GetRequiredService<IMjmlTemplateRenderer>();
    }

    [Fact]
    public async Task WelcomeEmail_NewUser() =>
        await VerifyTemplate("Welcome/NewUser", new Dictionary<string, string>
        {
            { "UserName", "John Doe" },
            { "LoginUrl", "https://example.com/login" }
        });

    [Fact]
    public async Task WelcomeEmail_InvitedUser() =>
        await VerifyTemplate("Welcome/InvitedUser", new Dictionary<string, string>
        {
            { "UserName", "John Doe" },
            { "InviterName", "Jane Admin" },
            { "OrganizationName", "Acme Corp" }
        });

    [Fact]
    public async Task PasswordReset() =>
        await VerifyTemplate("PasswordReset/PasswordReset", new Dictionary<string, string>
        {
            { "UserName", "John Doe" },
            { "ResetLink", "https://example.com/reset/abc123" },
            { "ExpirationMinutes", "30" }
        });

    [Fact]
    public async Task PaymentReceipt() =>
        await VerifyTemplate("Billing/PaymentReceipt", new Dictionary<string, string>
        {
            { "UserName", "John Doe" },
            { "Amount", "$10.00" },
            { "InvoiceNumber", "INV-2025-001" },
            { "Date", "January 15, 2025" }
        });

    private async Task VerifyTemplate(
        string templateName,
        Dictionary<string, string> variables)
    {
        var html = await _renderer.RenderTemplateAsync(templateName, variables);
        await Verify(html, extension: "html")
            .UseMethodName(templateName.Replace("/", "_"));
    }
}
```

---

## Scrubbing Dynamic Values

Some values change between test runs. Scrub them:

```csharp
[Fact]
public async Task EmailWithTimestamp_ScrubsDynamicValues()
{
    var html = await _renderer.RenderTemplateAsync("Welcome", variables);

    await Verify(html, extension: "html")
        .ScrubLinesContaining("Generated at:")
        .ScrubInlineGuids();  // Scrubs GUIDs in URLs
}
```

### Common Scrubbers

```csharp
// Scrub dates
.ScrubLinesContaining("Date:")
.AddScrubber(s => Regex.Replace(s, @"\d{4}-\d{2}-\d{2}", "SCRUBBED-DATE"))

// Scrub URLs with tokens
.AddScrubber(s => Regex.Replace(s, @"token=[a-zA-Z0-9]+", "token=SCRUBBED"))

// Scrub GUIDs
.ScrubInlineGuids()
```

---

## Test Fixture for Email Tests

```csharp
public class EmailTestFixture : IAsyncLifetime
{
    public IServiceProvider Services { get; private set; } = null!;

    public async Task InitializeAsync()
    {
        var services = new ServiceCollection();

        services.AddSingleton<IConfiguration>(new ConfigurationBuilder()
            .AddInMemoryCollection(new Dictionary<string, string?>
            {
                ["SiteUrl"] = "https://example.com"
            })
            .Build());

        services.AddSingleton<IMjmlTemplateRenderer, MjmlTemplateRenderer>();

        Services = services.BuildServiceProvider();

        await Task.CompletedTask;
    }

    public Task DisposeAsync() => Task.CompletedTask;
}
```

---

## Composer Snapshot Tests

Test the full composer output including subject and metadata:

```csharp

Excerpt, first 6,000 characters of SKILL.md, verbatim from the audited commit. It is text from someone else’s repository, quoted so you can judge it before your agent reads it.

git clone https://github.com/Aaronontheweb/dotnet-skills
git -C dotnet-skills checkout 871f73ffcae3

Works in

1. 2026-10-18
   ✓SAFE B 89 / 100

   first audit · source 871f73ffcae3

Questions about Verify Email Snapshots

• github.com/Aaronontheweb/dotnet-skills/tree/master/skills/verify — the audited source at commit 871f73ffcae3 and every finding aboveObserved · 18 Oct 2026

Spotted something wrong? Report a correction · Methodology