如何在NSubstitute中Mock属性setter，解决VB.NET场景下的匹配问题

解决方案 #

1. 写法错误修正

你原有代码的模式选择器使用Function定义，会被NSubstitute识别为「获取属性值后做相等比较」的表达式，无法匹配setter调用。需要改为Sub定义赋值操作，让框架正确识别你要匹配的是索引属性的setter。

2. CallInfo参数获取规则

索引属性的setter包含两个输入参数：第0位为你定义的索引值i As ULong，第1位为要设置的属性值T，可直接通过CallInfo的泛型方法提取。

完整可运行代码如下：

Public Interface IDAO(Of T) : Inherits IDAO
    Default Property Value(i As ULong) As T
    Function Append(ts As ICollection(Of T)) As ULong
    Function Remove(f As Predicate(Of T)) As ICollection(Of T)
    Function GetRestricted(f As Predicate(Of T)) As ICollection(Of T)
    Function RemoveFirst(f As Predicate(Of T)) As T
    Function GetFirst(f As Predicate(Of T)) As T
End Interface
'...
_mock.WhenForAnyArgs(
    Sub(mock As IDAO(Of T)) mock.Value(Arg.Any(Of ULong)) = Arg.Any(Of T)()
).Do(
    Sub(c As Core.CallInfo)
        ' 提取setter的两个参数
        Dim index As ULong = c.Arg(Of ULong)(0)
        Dim setValue As T = c.Arg(Of T)(1)
        ' 执行你需要的自定义逻辑
        _inner.data(index) = setValue
    End Sub
)

如果需要针对特定索引匹配setter，把Arg.Any(Of ULong)替换为对应固定值即可。

内容的提问来源于stack exchange，提问作者user13507303