使用 Expression 为方法设置模拟

Question

我正在尝试为方法设置模拟的 return 值。我知道这样做的经典方法，但我想通过显式创建 Expression 对象来做到这一点。到目前为止，这是我尝试过的方法：

using Moq;
using NUnit.Framework;
using System;
using System.Linq.Expressions;

namespace MoqTest
{
    public interface IBlah
    {
        string DoStuff(string x);
    }

    public class SomeProgram
    {
        static void Main(string[] args)
        {
            Mock<IBlah> m = new Mock<IBlah>(MockBehavior.Strict);

            //I want to do the equivalent of this:
            //m.Setup(a => a.DoStuff(It.IsAny<string>())).Returns("mocked!");

            var method = typeof(IBlah).GetMethod("DoStuff", new Type[] { typeof(string) });
            ParameterExpression parameterForDoStuff = Expression.Parameter(typeof(string), "x");
            ParameterExpression thisParameter = Expression.Parameter(typeof(IBlah), "someIBlahInstance");
            MethodCallExpression methodCall = Expression.Call(thisParameter, method, new[] { parameterForDoStuff });
            Expression<Func<IBlah, string>> lambdaExpression = Expression.Lambda<Func<IBlah, string>>(methodCall, new ParameterExpression[] { parameterForDoStuff });
            //above line fails: Unhandled Exception: System.ArgumentException: ParameterExpression of type 'System.String' cannot be used for delegate parameter of type 'MoqTest.IBlah'

            m.Setup(lambdaExpression).Returns("mocked!");

            Assert.AreEqual("mocked!", m.Object.DoStuff(string.Empty));
        }
    }
}

如您所见，我对 lambdaExpression 感到困惑 - 我应该创建一个代表 Func<string,string> 的表达式（对于 IBlah.DoStuff 方法），还是应该创建a Func<IBlah,string>（代表 Mock.Setup 方法的 lambda 参数）？我把我想做的等效设置放在代码的注释中。

Answer 1

您应该创建一个 Expression<Func<IBlah, string>> 表示 Mock.Setup 方法的表达式参数。

也就是说参数表达式应该只有一个。

此外，在构建所需的表达式时，It.IsAny<T>() 是对静态 class Moq.It.

的通用静态方法调用

查看评论以了解如何使用反射将静态调用构建到表达式中。

[TestClass]
public class MoqExpressionTests {
    [TestMethod]
    public void Should_Build_Moq_Expression() {
        //Arrange
        //I want to do the equivalent of this:
        //m.Setup(a => a.DoStuff(It.IsAny<string>())).Returns("mocked!");
        var doStuff = typeof(IBlah).GetMethod("DoStuff", new Type[] { typeof(string) });
        var isAnyOfString = typeof(It).GetMethod("IsAny").MakeGenericMethod(typeof(string));

        // IBlah x =>
        ParameterExpression parameter = Expression.Parameter(typeof(IBlah), "x");
        // It.IsAny<string>()            
        var arg = Expression.Call(isAnyOfString);
        // IBlah x => x.DoStuff(It.IsAny<string>())           
        MethodCallExpression body = Expression.Call(parameter, doStuff, new[] { arg });
        //Func<IBlah, string> = IBlah x => x.DoStuff(It.IsAny<string>())
        Expression<Func<IBlah, string>> expression = 
            Expression.Lambda<Func<IBlah, string>>(body, parameter);

        var expected = "mocked!";
        Mock<IBlah> m = new Mock<IBlah>(MockBehavior.Strict);
        m.Setup(expression).Returns(expected);
        var subject = m.Object;

        //Act
        var actual = subject.DoStuff(string.Empty);

        //Assert
        Assert.AreEqual(expected, actual);
    }

    public interface IBlah {
        string DoStuff(string x);
    }
}

Answer 2

你不能为 It.IsAny 使用字符串参数，需要使用 MethodCallExpression

对于lambdaExpression表达式第二个参数应该是这个参数。

public class SomeProgram
{
    static void Main(string[] args)
    {
        Mock<IBlah> m = new Mock<IBlah>(MockBehavior.Strict);

        //I want to do the equivalent of this:
        //m.Setup(a => a.DoStuff(It.IsAny<string>())).Returns("mocked!");

        var method = typeof(IBlah).GetMethod("DoStuff", new Type[] { typeof(string) });
        MethodInfo genericIsAnyMethodInfo =
            typeof(It).GetMethods().Single(e => e.Name == "IsAny").MakeGenericMethod(typeof(string));
        MethodCallExpression parameterForDoStuff = Expression.Call(genericIsAnyMethodInfo);
        //ParameterExpression parameterForDoStuff = Expression.Parameter(typeof(string), "x");
        ParameterExpression thisParameter = Expression.Parameter(typeof(IBlah), "someIBlahInstance");
        MethodCallExpression methodCall = Expression.Call(thisParameter, method, new[] { parameterForDoStuff });
        Expression<Func<IBlah, string>> lambdaExpression = Expression.Lambda<Func<IBlah, string>>(methodCall, thisParameter);
        //above line fails: Unhandled Exception: System.ArgumentException: ParameterExpression of type 'System.String' cannot be used for delegate parameter of type 'MoqTest.IBlah'

        m.Setup(lambdaExpression).Returns("mocked!");

        Assert.AreEqual("mocked!", m.Object.DoStuff(string.Empty));
    }
}

使用 Expression 为方法设置模拟

Setup a mock for a method using Expression

c#

linq

moq