dotnet-playwright

dotnet-playwright

Playwright for .NET: browser automation and end-to-end testing. Covers browser lifecycle management, page interactions, assertions, CI caching of browser binaries, trace viewer for debugging failures, and codegen for rapid test scaffolding.

Version assumptions: Playwright 1.40+ for .NET, .NET 8.0+ baseline. Playwright supports Chromium, Firefox, and WebKit browsers.

Out of scope: Shared UI testing patterns (page object model, selectors, wait strategies) are in [skill:dotnet-ui-testing-core]. Testing strategy (when E2E vs unit vs integration) is covered by [skill:dotnet-testing-strategy]. Test project scaffolding is owned by [skill:dotnet-add-testing].

Prerequisites: Test project scaffolded via [skill:dotnet-add-testing] with Playwright packages referenced. Browsers installed via pwsh bin/Debug/net8.0/playwright.ps1 install or dotnet tool run playwright install.

Cross-references: [skill:dotnet-ui-testing-core] for page object model and selector strategies, [skill:dotnet-testing-strategy] for deciding when E2E tests are appropriate.

---

Package Setup

<PackageReference Include="Microsoft.Playwright" Version="1.*" />
<!-- For xUnit integration: -->
<PackageReference Include="Microsoft.Playwright.Xunit" Version="1.*" />
<!-- For NUnit integration: -->
<!-- <PackageReference Include="Microsoft.Playwright.NUnit" Version="1.*" /> -->

Installing Browsers

Playwright requires downloading browser binaries before tests can run:

# After building the test project:
pwsh bin/Debug/net8.0/playwright.ps1 install

# Or install specific browsers:
pwsh bin/Debug/net8.0/playwright.ps1 install chromium
pwsh bin/Debug/net8.0/playwright.ps1 install firefox

# Using dotnet tool:
dotnet tool install --global Microsoft.Playwright.CLI
playwright install

---

Basic Test Structure

With Playwright xUnit Base Class

using Microsoft.Playwright;
using Microsoft.Playwright.Xunit;

// PageTest provides Page, Browser, BrowserContext, and Playwright properties
public class HomePageTests : PageTest
{
    [Fact]
    public async Task HomePage_Title_ContainsAppName()
    {
        await Page.GotoAsync("https://localhost:5001");

        await Expect(Page).ToHaveTitleAsync(new Regex("My App"));
    }

    [Fact]
    public async Task HomePage_NavLinks_AreVisible()
    {
        await Page.GotoAsync("https://localhost:5001");

        var nav = Page.Locator("nav");
        await Expect(nav.GetByRole(AriaRole.Link, new() { Name = "Home" }))
            .ToBeVisibleAsync();
        await Expect(nav.GetByRole(AriaRole.Link, new() { Name = "About" }))
            .ToBeVisibleAsync();
    }
}

Manual Setup (Without Base Class)

public class ManualSetupTests : IAsyncLifetime
{
    private IPlaywright _playwright = null!;
    private IBrowser _browser = null!;
    private IBrowserContext _context = null!;
    private IPage _page = null!;

    public async ValueTask InitializeAsync()
    {
        _playwright = await Playwright.CreateAsync();
        _browser = await _playwright.Chromium.LaunchAsync(new BrowserTypeLaunchOptions
        {
            Headless = true
        });
        _context = await _browser.NewContextAsync(new BrowserNewContextOptions
        {
            ViewportSize = new ViewportSize { Width = 1280, Height = 720 },
            Locale = "en-US"
        });
        _page = await _context.NewPageAsync();
    }

    public async ValueTask DisposeAsync()
    {
        await _page.CloseAsync();
        await _context.CloseAsync();
        await _browser.CloseAsync();
        _playwright.Dispose();
    }

    [Fact]
    public async Task Login_ValidUser_RedirectsToDashboard()
    {
        await _page.GotoAsync("https://localhost:5001/login");

        await _page.FillAsync("[data-testid='email']", "[email protected]");
        await _page.FillAsync("[data-testid='password']", "P@ssw0rd!");
        await _page.ClickAsync("[data-testid='login-btn']");

        await Expect(_page).ToHaveURLAsync(new Regex("/dashboard"));
    }
}

---

Locators and Interactions

Recommended Locator Strategies

// BEST: Role-based (accessible and semantic)
var submitBtn = Page.GetByRole(AriaRole.Button, new() { Name = "Submit Order" });

// GOOD: Test ID (stable, explicit)
var emailInput = Page.Locator("[data-testid='email-input']");

// GOOD: Label text (user-visible, accessible)
var nameField = Page.GetByLabel("Full Name");

// GOOD: Placeholder (user-visible)
var searchBox = Page.GetByPlaceholder("Search products...");

// AVOID: CSS class (fragile, changes with styling)
var card = Page.Locator(".card-primary");

// AVOID: XPath (brittle, hard to read)
var cell = Page.Locator("//table/tbody/tr[1]/td[2]");

Common Interactions

// Text input
await Page.FillAsync("[data-testid='name']", "Alice Johnson");

// Click
await Page.ClickAsync("[data-testid='submit']");

// Select dropdown
await Page.SelectOptionAsync("[data-testid='country']", "US");

// Checkbox / radio
await Page.CheckAsync("[data-testid='agree-terms']");

// File upload
await Page.SetInputFilesAsync("[data-testid='avatar']", "testdata/photo.jpg");

// Keyboard
await Page.Keyboard.PressAsync("Enter");
await Page.Keyboard.TypeAsync("search query");

// Hover (for dropdowns, tooltips)
await Page.HoverAsync("[data-testid='user-menu']");

Assertions (Expect API)

Playwright assertions auto-retry until the condition is met or the timeout expires:

// Element visibility
await Expect(Page.Locator("[data-testid='success']")).ToBeVisibleAsync();
await Expect(Page.Locator("[data-testid='spinner']")).ToBeHiddenAsync();

// Text content
await Expect(Page.Locator("[data-testid='total']")).ToHaveTextAsync("$99.99");
await Expect(Page.Locator("[data-testid='status']")).ToContainTextAsync("Completed");

// Attribute
await Expect(Page.Locator("[data-testid='submit']")).ToBeEnabledAsync();
await Expect(Page.Locator("[data-testid='email']")).ToHaveValueAsync("[email protected]");

// Page-level
await Expect(Page).ToHaveURLAsync(new Regex("/orders/\\d+"));
await Expect(Page).ToHaveTitleAsync("Order Details - My App");

// Count
await Expect(Page.Locator("[data-testid='order-row']")).ToHaveCountAsync(5);

---

Network Interception

Mocking API Responses

[Fact]
public async Task OrderList_WithMockedApi_DisplaysOrders()
{
    // Intercept API calls and return mock data
    await Page.RouteAsync("**/api/orders", async route =>
    {
        var json = JsonSerializer.Serialize(new[]
        {
            new { Id = 1, CustomerName = "Alice", Total = 99.99 },
            new { Id = 2, CustomerName = "Bob", Total = 149.50 }
        });
        await route.FulfillAsync(new RouteFulfillOptions
        {
            Status = 200,
            ContentType = "application/json",
            Body = json
        });
    });

    await Page.GotoAsync("https://localhost:5001/orders");

    await Expect(Page.Locator("[data-testid='order-row']")).ToHaveCountAsync(2);
}

Waiting for Network Requests

[Fact]
public async Task CreateOrder_SubmitForm_WaitsForApiResponse()
{
    await Page.GotoAsync("https://localhost:5001/orders/new");

    await Page.FillAsync("[data-testid='customer']", "Alice");
    await Page.FillAsync("[data-testid='amount']", "99.99");

    // Wait for the API call triggered by form submission
    var responseTask = Page.WaitForResponseAsync(
        response => response.Url.Contains("/api/orders") && response.Status == 201);

    await Page.ClickAsync("[data-testid='submit']");

    var response = await responseTask;
    Assert.Equal(201, response.Status);
}

---

CI Browser Caching

Downloading browser binaries on every CI run is slow (500MB+). Cache them to speed up builds.

GitHub Actions Caching

# .github/workflows/e2e-tests.yml
jobs:
  e2e:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - name: Setup .NET
        uses: actions/setup-dotnet@v4
        with:
          dotnet-version: '8.0.x'

      - name: Build
        run: dotnet build tests/MyApp.E2E/

      - name: Cache Playwright browsers
        id: playwright-cache
        uses: actions/cache@v4
        with:
          path: ~/.cache/ms-playwright
          key: playwright-${{ runner.os }}-${{ hashFiles('tests/MyApp.E2E/MyApp.E2E.csproj') }}

      - name: Install Playwright browsers
        if: steps.playwright-cache.outputs.cache-hit != 'true'
        run: pwsh tests/MyApp.E2E/bin/Debug/net8.0/playwright.ps1 install --with-deps

      - name: Install Playwright system deps
        if: steps.playwright-cache.outputs.cache-hit == 'true'
        run: pwsh tests/MyApp.E2E/bin/Debug/net8.0/playwright.ps1 install-deps

      - name: Run E2E tests
        run: dotnet test tests/MyApp.E2E/

Azure DevOps Caching

# azure-pipelines.yml
steps:
  - task: Cache@2
    inputs:
      key: 'playwright | "$(Agent.OS)" | tests/MyApp.E2E/MyApp.E2E.csproj'
      path: $(HOME)/.cache/ms-playwright
      restoreKeys: |
        playwright | "$(Agent.OS)"
      cacheHitVar: PLAYWRIGHT_CACHE_RESTORED
    displayName: Cache Playwright browsers

  - script: pwsh tests/MyApp.E2E/bin/Debug/net8.0/playwright.ps1 install --with-deps
    condition: ne(variables.PLAYWRIGHT_CACHE_RESTORED, 'true')
    displayName: Install Playwright browsers

  - script: pwsh tests/MyApp.E2E/bin/Debug/net8.0/playwright.ps1 install-deps
    condition: eq(variables.PLAYWRIGHT_CACHE_RESTORED, 'true')
    displayName: Install Playwright system deps (cached browsers)

  - script: dotnet test tests/MyApp.E2E/
    displayName: Run E2E tests

Cache Key Strategy

The cache key should include:

• OS: Browser binaries are platform-specific
• Project file hash: Playwright version determines browser versions; changing the package version invalidates the cache
• Fallback key: Allows partial cache restoration when the project file changes

---

Trace Viewer

Playwright's trace viewer captures a full recording of test execution for debugging failures. Each trace includes screenshots, DOM snapshots, network logs, and console output.

Enabling Traces

public class TracedTests : IAsyncLifetime
{
    private IPlaywright _playwright = null!;
    private IBrowser _browser = null!;
    private IBrowserContext _context = null!;

    public IPage Page { get; private set; } = null!;

    public async ValueTask InitializeAsync()
    {
        _playwright = await Playwright.CreateAsync();
        _browser = await _playwright.Chromium.LaunchAsync();
        _context = await _browser.NewContextAsync();

        // Start tracing before each test
        await _context.Tracing.StartAsync(new TracingStartOptions
        {
            Screenshots = true,
            Snapshots = true,
            Sources = true
        });

        Page = await _context.NewPageAsync();
    }

    public async ValueTask DisposeAsync()
    {
        // Save trace on failure (check test result in xUnit requires custom wrapper)
        await _context.Tracing.StopAsync(new TracingStopOptions
        {
            Path = Path.Combine("test-results", "traces",
                $"trace-{DateTime.UtcNow:yyyyMMdd-HHmmss}.zip")
        });

        await Page.CloseAsync();
        await _context.CloseAsync();
        await _browser.CloseAsync();
        _playwright.Dispose();
    }
}

Viewing Traces

# Open trace file in browser
pwsh bin/Debug/net8.0/playwright.ps1 show-trace test-results/traces/trace-20260101-120000.zip

# Or use the online trace viewer
# Upload the .zip to https://trace.playwright.dev/

Trace on Failure Only

Save traces only when tests fail to reduce storage:

// In a custom test class or middleware
public async Task RunWithTrace(Func<IPage, Task> testAction, string testName)
{
    await _context.Tracing.StartAsync(new TracingStartOptions
    {
        Screenshots = true,
        Snapshots = true,
        Sources = true
    });

    try
    {
        await testAction(Page);
        // Test passed -- discard trace
        await _context.Tracing.StopAsync();
    }
    catch
    {
        // Test failed -- save trace for debugging
        await _context.Tracing.StopAsync(new TracingStopOptions
        {
            Path = $"test-results/traces/{testName}.zip"
        });
        throw;
    }
}

---

Codegen

Playwright's code generator records browser interactions and generates test code. Use it to scaffold tests quickly, then refine the generated code.

Running Codegen

# Open codegen with your app URL
pwsh bin/Debug/net8.0/playwright.ps1 codegen https://localhost:5001

# With specific browser
pwsh bin/Debug/net8.0/playwright.ps1 codegen --browser firefox https://localhost:5001

# With device emulation
pwsh bin/Debug/net8.0/playwright.ps1 codegen --device "iPhone 15" https://localhost:5001

# With saved authentication state
pwsh bin/Debug/net8.0/playwright.ps1 codegen --save-storage auth.json https://localhost:5001

Codegen Best Practices

1. Use codegen as a starting point, not the final test. Generated code often uses fragile selectors and lacks proper assertions.
2. Replace generated selectors with data-testid or role-based locators immediately after generating.
3. Add meaningful assertions. Codegen records actions but does not know what to verify. Add Expect() calls for expected outcomes.
4. Extract page objects from generated code. Group related interactions into page object methods.

Before and After Codegen Refinement

// GENERATED by codegen (fragile, no assertions):
await page.GotoAsync("https://localhost:5001/orders");
await page.Locator("#root > div > main > div:nth-child(2) > button").ClickAsync();
await page.GetByPlaceholder("Customer name").FillAsync("Alice");
await page.GetByPlaceholder("Amount").FillAsync("99.99");
await page.Locator("form > button[type='submit']").ClickAsync();

// REFINED (stable selectors, proper assertions):
await Page.GotoAsync("https://localhost:5001/orders");
await Page.ClickAsync("[data-testid='new-order-btn']");
await Page.FillAsync("[data-testid='customer-name']", "Alice");
await Page.FillAsync("[data-testid='amount']", "99.99");
await Page.ClickAsync("[data-testid='submit-order']");

await Expect(Page.Locator("[data-testid='success-toast']"))
    .ToBeVisibleAsync();
await Expect(Page).ToHaveURLAsync(new Regex("/orders/\\d+"));

---

Multi-Browser Testing

Running Tests Across Browsers

// Using Playwright xUnit base class with environment variable
// Set BROWSER=chromium|firefox|webkit via CLI or CI config
public class CrossBrowserTests : PageTest
{
    [Fact]
    public async Task OrderFlow_WorksAcrossBrowsers()
    {
        // This test runs in whichever browser BROWSER env var specifies
        await Page.GotoAsync("https://localhost:5001/orders/new");
        await Page.FillAsync("[data-testid='customer']", "Alice");
        await Page.ClickAsync("[data-testid='submit']");

        await Expect(Page.Locator("[data-testid='success']")).ToBeVisibleAsync();
    }
}

# Run tests in each browser
BROWSER=chromium dotnet test
BROWSER=firefox dotnet test
BROWSER=webkit dotnet test

CI Matrix Strategy

# GitHub Actions matrix for multi-browser
strategy:
  matrix:
    browser: [chromium, firefox, webkit]
steps:
  - name: Run E2E tests
    run: dotnet test tests/MyApp.E2E/
    env:
      BROWSER: ${{ matrix.browser }}

---

Key Principles

• Use Playwright assertions (Expect) instead of raw xUnit Assert. Playwright assertions auto-retry with configurable timeouts, eliminating flaky timing issues.
• Cache browser binaries in CI. Downloading 500MB+ of browsers per run wastes time and bandwidth. Cache by OS + Playwright version.
• Enable trace viewer for debugging CI failures. Traces capture everything needed to reproduce a failure without re-running the test.
• Use codegen to bootstrap tests, then refine. Generated code gets you started fast; manual refinement makes tests maintainable.
• Prefer role-based or data-testid locators over CSS classes or XPath. See [skill:dotnet-ui-testing-core] for the full selector priority guide.

---

Agent Gotchas

1. Do not forget to install browsers after adding the Playwright package. The NuGet package does not include browser binaries. Run the install script after building.
2. Do not use Task.Delay for waiting. Playwright's auto-waiting and Expect assertions handle timing automatically. Adding delays makes tests slow and still flaky.
3. Do not hardcode localhost ports. Use configuration or environment variables for the base URL. CI environments may use different ports than local development.
4. Do not skip --with-deps on first CI install. Playwright browsers need system libraries (libgbm, libasound, etc.) on Linux. The --with-deps flag installs them. Subsequent cached runs only need install-deps.
5. Do not store trace files in the repository. Traces are large binary files. Write them to a test-results/ directory that is git-ignored, and upload them as CI artifacts.
6. Do not create a new browser instance per test. Browser launch is expensive. Use IClassFixture or the Playwright xUnit base class to share a browser across tests in a class. Create a new BrowserContext per test for isolation.

---

References

• Playwright for .NET Documentation
• Playwright Locators
• Playwright Assertions
• Playwright Trace Viewer
• Playwright Codegen
• Playwright CI Configuration
• Playwright Browser Downloads