snapshot-testing

使用 Verify 进行快照测试

何时使用此技能

在以下情况下使用快照测试：

• 验证渲染输出（HTML 邮件、报告、生成的代码）
• 审核公共 API 接口，以检测破坏性变更
• 测试 HTTP 响应正文和标头
• 验证序列化输出
• 发现复杂对象中的意外变更

---

什么是快照测试？

快照测试会捕获输出，并与经过人工审核的基准进行比较：

1. 首次运行：测试生成包含实际输出的 .received. 文件
2. 人工审核：开发者批准该文件，从而创建 .verified. 文件
3. 后续运行：测试将输出与 .verified. 文件进行比较
4. 检测到变更：测试失败，差异工具会显示差异供审核

这能发现意外变更，同时允许通过明确批准来接受有意变更。

---

安装

添加 Verify 包

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

配置 ModuleInitializer

在测试项目中创建 ModuleInitializer.cs：

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);
    }
}

---

基本用法

验证简单对象

[Fact]
public Task VerifyUserDto()
{
    var user = new UserDto(
        Id: "user-123",
        Name: "John Doe",
        Email: "[email protected]",
        CreatedAt: new DateTime(2025, 1, 15));

    return Verify(user);
}

创建 VerifyUserDto.verified.txt：

{
  Id: user-123,
  Name: John Doe,
  Email: [email protected],
  CreatedAt: 2025-01-15T00:00:00
}

验证字符串/HTML

[Fact]
public async Task VerifyRenderedEmail()
{
    var html = await _emailRenderer.RenderAsync("Welcome", new { Name = "John" });

    // Use extension parameter for proper file naming
    await Verify(html, extension: "html");
}

创建 VerifyRenderedEmail.verified.html，可在浏览器中查看。

---

邮件模板测试

使用 Verify 发现渲染后的邮件模板中的意外变更：

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

    var variables = new Dictionary<string, string>
    {
        { "OrganizationName", "Acme Corporation" },
        { "InviteeName", "John Doe" },
        { "InviterName", "Jane Admin" },
        { "InvitationLink", "https://example.com/invite/abc123" },
        { "ExpirationDate", "December 31, 2025" }
    };

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

    await Verify(html, extension: "html");
}

邮件测试的优势：

• 发现 CSS/布局回归
• 检测模板变量失效
• 在差异工具中进行可视化审核
• 通过版本控制跟踪邮件变更

---

API 接口审核

防止公共 API 发生意外的破坏性变更：

[Fact]
public Task ApprovePublicApi()
{
    var assembly = typeof(MyLibrary.PublicClass).Assembly;

    var publicApi = assembly.GetExportedTypes()
        .OrderBy(t => t.FullName)
        .Select(t => new
        {
            Type = t.FullName,
            Members = t.GetMembers(BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static)
                .Where(m => m.DeclaringType == t)
                .OrderBy(m => m.Name)
                .Select(m => m.ToString())
        });

    return Verify(publicApi);
}

也可以使用专用的 ApiApprover 包：

dotnet add package PublicApiGenerator
dotnet add package Verify.Xunit

[Fact]
public Task ApproveApi()
{
    var api = typeof(MyPublicClass).Assembly.GeneratePublicApi();
    return Verify(api);
}

创建包含完整 API 接口的 .verified.txt；任何变更都需要明确批准。

---

HTTP 响应测试

[Fact]
public async Task GetUser_ReturnsExpectedResponse()
{
    var client = _factory.CreateClient();

    var response = await client.GetAsync("/api/users/123");

    // Verify status, headers, and body together
    await Verify(new
    {
        StatusCode = response.StatusCode,
        Headers = response.Headers
            .Where(h => h.Key.StartsWith("X-"))  // Custom headers only
            .ToDictionary(h => h.Key, h => h.Value.First()),
        Body = await response.Content.ReadAsStringAsync()
    });
}

---

清理动态值

处理时间戳、GUID 和其他动态内容：

[Fact]
public Task VerifyOrder()
{
    var order = new Order
    {
        Id = Guid.NewGuid(),  // Different every run
        CreatedAt = DateTime.UtcNow,  // Different every run
        Total = 99.99m
    };

    return Verify(order)
        .ScrubMember("Id")  // Replace with placeholder
        .ScrubMember("CreatedAt");
}

输出：

{
  Id: Guid_1,
  CreatedAt: DateTime_1,
  Total: 99.99
}

全局清理

在 ModuleInitializer 中配置：

[ModuleInitializer]
public static void Init()
{
    VerifierSettings.ScrubMembersWithType<DateTime>();
    VerifierSettings.ScrubMembersWithType<DateTimeOffset>();
    VerifierSettings.ScrubMembersWithType<Guid>();

    // Scrub specific patterns
    VerifierSettings.AddScrubber(s =>
        Regex.Replace(s, @"token=[a-zA-Z0-9]+", "token=SCRUBBED"));
}

---

文件组织

推荐结构

tests/
  MyApp.Tests/
    Snapshots/           # All verified files
      EmailTests/
        WelcomeEmail.verified.html
        PasswordReset.verified.html
      ApiTests/
        GetUser.verified.txt
    EmailTests.cs
    ApiTests.cs
    ModuleInitializer.cs

.gitignore

# Verify - ignore received files (only commit verified)
*.received.*

.gitattributes

# Treat verified files as generated (collapse in PR diffs)
*.verified.txt linguist-generated=true
*.verified.html linguist-generated=true
*.verified.json linguist-generated=true

---

CI/CD 集成

缺少已验证文件时失败

[ModuleInitializer]
public static void Init()
{
    // In CI, fail instead of launching diff tool
    if (Environment.GetEnvironmentVariable("CI") == "true")
    {
        VerifyDiffPlex.UseDiffPlex(OutputType.Minimal);
        DiffRunner.Disabled = true;
    }
}

GitHub Actions

- name: Run tests
  run: dotnet test
  env:
    CI: true

- name: Upload snapshots on failure
  if: failure()
  uses: actions/upload-artifact@v4
  with:
    name: snapshots
    path: |
      **/*.received.*
      **/*.verified.*

---

何时使用快照测试

场景	使用快照测试？	原因
渲染后的 HTML/邮件	是	发现视觉回归
API 接口	是	防止意外破坏
序列化输出	是	验证传输格式
复杂对象图	是	比手动断言更简单
简单值检查	否	使用常规断言
业务逻辑	否	使用明确的断言
性能测试	否	使用基准测试

---

最佳实践

应该做

// Use descriptive test names - they become file names
[Fact]
public Task UserRegistration_WithValidData_ReturnsConfirmation()

// Scrub dynamic values consistently
VerifierSettings.ScrubMembersWithType<Guid>();

// Use extension parameter for non-text content
await Verify(html, extension: "html");

// Keep verified files in source control
git add *.verified.*

不应该做

// Don't verify random/dynamic data without scrubbing
var order = new Order { Id = Guid.NewGuid() };  // Fails every run!
await Verify(order);

// Don't commit .received files
git add *.received.*  // Wrong!

// Don't use for simple assertions
await Verify(result.Count);  // Just use Assert.Equal(5, result.Count)

---

与 MJML 邮件测试集成

有关完整模式，请参阅 mjml-email-templates 和 verify-email-snapshots 技能：

1. 使用 {{variable}} 占位符的 MJML 模板
2. 使用测试数据渲染为 HTML
3. 对渲染后的输出进行快照测试
4. 批准前在差异工具中审核变更

这有助于发现：

• 变量替换失效
• CSS/布局回归
• 邮件客户端兼容性问题
• 意外的内容变更

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资源

• Verify GitHub：https://github.com/VerifyTests/Verify
• Verify.Xunit：https://github.com/VerifyTests/Verify.Xunit
• ApiApprover：https://github.com/JakeGinnivan/ApiApprover
• DiffPlex 集成：https://github.com/VerifyTests/Verify.DiffPlex