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Culture

The [Culture] attribute sets the current Culture for the duration of a test. It can be applied at the test, class, or assembly level. The culture is restored to its original value when the test completes.

Why This Matters​

Different locales format numbers, dates, and currencies differently. A test that passes on a developer's machine in the US may fail on a CI server in Germany if it parses or compares formatted strings. The [Culture] attribute locks the culture so results are predictable regardless of where the tests run.

Without [Culture] — this test passes in en-US but fails in de-AT (where the decimal separator is ,):

[Test]
public async Task Fragile_Without_Culture()
{
    // Fails in locales where "3.5" is not a valid double literal
    var value = double.Parse("3.5");
    await Assert.That(value).IsEqualTo(3.5);
}

With [Culture] — the test is stable everywhere:

[Test, Culture("en-US")]
public async Task Stable_With_Culture()
{
    var value = double.Parse("3.5");
    await Assert.That(value).IsEqualTo(3.5);
}

Examples​

Test-Level Culture​

using TUnit.Core;

namespace MyTestProject;

public class MyTestClass
{
    [Test, Culture("de-AT")]
    public async Task Parse_German_Decimal()
    {
        await Assert.That(double.Parse("3,5")).IsEqualTo(3.5);
    }
}

Class-Level Culture​

Apply the attribute to the class to set the culture for every test in that fixture:

[Culture("fr-FR")]
public class FrenchFormattingTests
{
    [Test]
    public async Task Currency_Format()
    {
        var formatted = 1234.56.ToString("C");
        await Assert.That(formatted).Contains("1");
    }
}

Assembly-Level Culture​

Lock the culture for the entire test assembly:

[assembly: Culture("en-US")]

Notes​

  • Only one culture can be specified per scope. To run the same test under multiple cultures, factor out the test logic into a private method and call it from separate test methods, each with its own [Culture] attribute.
  • The attribute sets both CurrentCulture and CurrentUICulture for the executing thread.

See Also​