如何在xUnit中复用跨测试套件的测试用例？

针对你遇到的需要在多个测试套件中复用Widget验证逻辑的场景，xUnit提供了多种无需依赖继承的实现方式，以下是实用的几种方案：

1. 封装静态测试逻辑类 #

将Widget的验证断言逻辑抽离到独立的静态类中，在任意测试类中直接调用，避免重复编写断言代码：

共享测试逻辑类 #

public static class WidgetValidationAssertions
{
    // 验证Widget Id为null时的错误
    public static void ShouldRejectNullId(ValidationResult result, string propertyPath = nameof(Widget.Id))
    {
        Assert.False(result.IsValid);
        Assert.Contains(result.Errors, e => 
            e.PropertyName == propertyPath && 
            e.ErrorMessage == "Id cannot be null.");
    }

    // 验证Widget Id为0时的错误
    public static void ShouldRejectZeroId(ValidationResult result, string propertyPath = nameof(Widget.Id))
    {
        Assert.False(result.IsValid);
        Assert.Contains(result.Errors, e => 
            e.PropertyName == propertyPath && 
            e.ErrorMessage == "Id cannot be zero.");
    }

    // 验证Widget Name为null时的错误
    public static void ShouldRejectNullName(ValidationResult result, string propertyPath = nameof(Widget.Name))
    {
        Assert.False(result.IsValid);
        Assert.Contains(result.Errors, e => 
            e.PropertyName == propertyPath && 
            e.ErrorMessage == "Name cannot be null.");
    }
}

在WidgetValidatorTests中使用 #

public class WidgetValidatorTests
{
    private readonly WidgetValidator _validator = new WidgetValidator();

    [Fact]
    public void When_Id_Is_Null_Validation_Fails()
    {
        var widget = new Widget { Id = null };
        var result = _validator.Validate(widget);
        WidgetValidationAssertions.ShouldRejectNullId(result);
    }

    [Fact]
    public void When_Id_Is_Zero_Validation_Fails()
    {
        var widget = new Widget { Id = 0 };
        var result = _validator.Validate(widget);
        WidgetValidationAssertions.ShouldRejectZeroId(result);
    }
}

在WidgetInventoryValidatorTests中使用 #

针对RuleForEach的验证，只需构造包含问题Widget的Inventory实例，然后调用共享断言（注意属性路径要对应集合索引）：

public class WidgetInventoryValidatorTests
{
    private readonly WidgetInventoryValidator _validator = new WidgetInventoryValidator();

    [Fact]
    public void When_Widget_In_Inventory_Has_Null_Id_Validation_Fails()
    {
        var inventory = new WidgetInventory
        {
            Id = 1,
            Name = "Test Stock",
            Widgets = new List<Widget> { new Widget { Id = null } }
        };

        var result = _validator.Validate(inventory);
        WidgetValidationAssertions.ShouldRejectNullId(result, "Widgets[0].Id");
    }
}

2. 共享参数化测试数据（配合Theory） #

如果是参数化测试，可以把测试用例数据抽成共享集合，用[MemberData]在多个测试类中复用：

共享测试数据类 #

public static class WidgetTestCases
{
    public static IEnumerable<object[]> InvalidWidgetScenarios => new List<object[]>
    {
        new object[] { new Widget { Id = null }, "Id cannot be null.", nameof(Widget.Id) },
        new object[] { new Widget { Id = 0 }, "Id cannot be zero.", nameof(Widget.Id) },
        new object[] { new Widget { Name = null }, "Name cannot be null.", nameof(Widget.Name) }
    };
}

在WidgetValidatorTests中使用 #

public class WidgetValidatorTests
{
    private readonly WidgetValidator _validator = new WidgetValidator();

    [Theory]
    [MemberData(nameof(WidgetTestCases.InvalidWidgetScenarios))]
    public void Invalid_Widget_Should_Fail_Validation(Widget widget, string expectedMessage, string propertyName)
    {
        var result = _validator.Validate(widget);
        Assert.False(result.IsValid);
        Assert.Contains(result.Errors, e => 
            e.PropertyName == propertyName && 
            e.ErrorMessage == expectedMessage);
    }
}

在WidgetInventoryValidatorTests中使用 #

public class WidgetInventoryValidatorTests
{
    private readonly WidgetInventoryValidator _validator = new WidgetInventoryValidator();

    [Theory]
    [MemberData(nameof(WidgetTestCases.InvalidWidgetScenarios))]
    public void Inventory_With_Invalid_Widget_Should_Fail(Widget invalidWidget, string expectedMessage, string propertyName)
    {
        var inventory = new WidgetInventory
        {
            Id = 1,
            Name = "Test Stock",
            Widgets = new List<Widget> { invalidWidget }
        };

        var result = _validator.Validate(inventory);
        Assert.False(result.IsValid);
        // 构造集合属性路径
        var collectionPropertyPath = $"Widgets[0].{propertyName}";
        Assert.Contains(result.Errors, e => 
            e.PropertyName == collectionPropertyPath && 
            e.ErrorMessage == expectedMessage);
    }
}

3. 可选：用IClassFixture共享验证器实例 #

如果需要在多个测试类中复用同一个验证器实例（避免重复初始化），可以结合xUnit的IClassFixture接口，但这通常是辅助优化，配合上面的逻辑使用：

public class WidgetValidatorFixture
{
    public WidgetValidator Validator { get; } = new WidgetValidator();
}

// 在测试类中使用Fixture
public class WidgetValidatorTests : IClassFixture<WidgetValidatorFixture>
{
    private readonly WidgetValidator _validator;

    public WidgetValidatorTests(WidgetValidatorFixture fixture)
    {
        _validator = fixture.Validator;
    }

    // 测试方法...
}

内容的提问来源于stack exchange，提问作者baynezy