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E2EE2E for .NET

Three languages

The app is tester-army/e2e-i18n: a Nuxt contact form in English, German, and Spanish. It reads the browser’s Accept-Language, so there is one URL and no cookie. This guide runs one test class once per language.

Run the app

Section titled “Run the app”
Terminal window
git clone https://github.com/tester-army/e2e-i18n
cd e2e-i18n
npm install
npm run dev        # http://localhost:3000

Set the browser’s language

Section titled “Set the browser’s language”

WebEngineOptions.Locale sets navigator.language and Accept-Language for every attempt. Override CreateEngine() and give the fixture one language per run:

using E2E.Engine;
using E2E.NUnit;


[TestFixture("en-US", "en", "English")]
[TestFixture("de-DE", "de", "German")]
[TestFixture("es-ES", "es", "Spanish")]
public sealed class ContactFormTests(string locale, string code, string language) : E2ETest
{
    protected override IEngine CreateEngine() => new WebEngine(new WebEngineOptions { Locale = locale });
}

TimezoneId (for example Europe/Berlin) works the same way when the app formats dates.

Tests that read no text

Section titled “Tests that read no text”

A test id and an attribute are the same in every language, so these tests need no model:

[Test]
public async Task The_page_is_in_the_browsers_language()
{
    await App.OpenAsync("/");


    Assert.That(await Browser.EvaluateAsync<string>("() => document.documentElement.lang"), Is.EqualTo(code));
    await Expect.That(Screen.GetByTestId($"language-{code}")).ToHaveAttributeAsync("aria-current", "true");
}


[Test]
public async Task Sending_an_empty_form_marks_every_required_field()
{
    await App.OpenAsync("/");
    await Expect.That(Screen.GetByTestId("send")).ToBeEnabledAsync();   // on once the page hydrates


    await Screen.GetByTestId("send").ClickAsync();


    await Expect.Poll(() => Browser.EvaluateAsync<int>("() => document.querySelectorAll('[aria-invalid=\"true\"]').length"))
        .ToBeAsync(3);
}

One agent test, written once in English

Section titled “One agent test, written once in English”

Give each language a persona in e2e.config.json, named by its code. A step that names a persona with ActOptions.Agent or AssertOptions.Agent goes to that agent, which reads the page in its language:

{
  "targets": [{ "name": "web", "platform": "web", "app": { "url": "http://localhost:3000" } }],
  "agents": {
    "default": { "provider": "copilot", "model": "claude-sonnet-5.5" },
    "de": {
      "provider": "copilot",
      "model": "claude-sonnet-5.5",
      "system": "You are a native German speaker using this page. Find your way by its German labels.",
      "context": "The page is a contact form: name, email, topic, message, and a send button. The browser is set to German."
    }
  }
}

Add an en and an es entry the same way. Then the test is the same in every language:

[Test]
[Category("RealModel")]
public async Task Sends_the_contact_form()
{
    await App.OpenAsync("/");
    await Expect.That(Screen.GetByTestId("send")).ToBeEnabledAsync();
    var ada = new Dictionary<string, object?>
    {
        ["name"] = "Ada Lovelace",
        ["email"] = "ada@example.com",
        ["message"] = "Hello from the e2e tests.",
    };


    await Agent.ActAsync(
        "fill in the contact form as {name} ({email}) with a bug report that says {message}, without sending it",
        new ActOptions { Agent = code, Params = ada });
    await Agent.ActAsync("send the message", new ActOptions { Agent = code });


    await Expect.That(Screen.GetByTestId("sent")).ToContainTextAsync("Ada Lovelace");
    await Agent.AssertAsync(
        $"The page says in {language} that the message was sent, thanks Ada Lovelace, and replies to ada@example.com",
        new AssertOptions { Agent = code });
}

Each persona records its own replay entries, so a second run replays every language with no model call.

Run

Section titled “Run”
Terminal window
dotnet test --project .                                          # all three languages
dotnet test --project . --filter "TestCategory!=RealModel"       # no model needed

Not covered here

Section titled “Not covered here”

The upstream repository also stores a screenshot per language and measures text that is wider than its box. Both are possible with ToHaveScreenshotAsync and Browser.EvaluateAsync, and are left out to keep this guide short.