Using C# Moq testing getting Parameter count mismatch?

Question

I know there are similar questions but somehow I am not able to figure out the situation in my case. I am getting Paramater count mismatch exception.

Here is how I am registering my Mock,

    var couponService = 
     DependencyResolver.Resolve<Mock<ICouponWebServiceAdapter>>();
        couponService.Setup(a => 
     a.checkCouponAvailability(It.IsAny<orderLine[]>(), 
            It.IsAny<orderHeader>()))
            .Returns((couponDetail[] request) =>
            {

                var coupon = new couponDetail
                {
                    description = "75% off the original price",
                    value = 50
                };

                var coupon1 = new couponDetail
                {
                    description = "500 off the original price",
                    value = 20
                };

                var coupondetails = new couponDetail[] { coupon, coupon1 };
                return coupondetails;
            });

the checkCouponAvailability is returning couponDetail[]

What am I doing wrong? I tried putting my return as IQueryable

Answer 1

It appears that inside of the Returns method you are specifying a parameter called request of type couponDetail[], yet the method itself takes the parameters of (orderLine[], orderHeader). The method that is passed into Returns gets invoked with the actual parameters that are passed into your mocked method which will cause the ParameterCountMismatchException you are getting.

1. You can pass in the literal object you want by mocking your return before mocking the function. Example below:

var coupondetails = new couponDetail[] {
    new couponDetail
    {
        description = "75% off the original price",
        value = 50
    },
    new couponDetail
    {
        description = "500 off the original price",
        value = 20
    }
};
var couponService = DependencyResolver.Resolve<Mock<ICouponWebServiceAdapter>>();

couponService
    .Setup(a => a.checkCouponAvailability(It.IsAny<orderLine[]>(), It.IsAny<orderHeader>()))
    .Returns(coupondetails);

2. You can pass a method to returns which MUST take all of the arguments passed into the original method. Example below:

var couponService = DependencyResolver.Resolve<Mock<ICouponWebServiceAdapter>>();

couponService
    .Setup(a => a.checkCouponAvailability(It.IsAny<orderLine[]>(), It.IsAny<orderHeader>()))
    .Returns((orderLine[] arg1, orderHeader arg2) => {
        return new couponDetail[] {
            new couponDetail
            {
                description = "75% off the original price",
                value = 50
            },
            new couponDetail
            {
                description = "500 off the original price",
                value = 20
            }
        };
    });