How to auto setup MOQ by given parameters and result in an object[]? - moq

Question

I want to automate the Setup code by a given array containing expected result and parameters.
Something like data driven setup.
My existing code:
var mock = new Mock<ILogin>();
var testDataTable = new object[,]
{
{ LoginResult.Success, "Jack", "123!##"}
, { LoginResult.WrongPassword, "Jack", "123321"}
, { LoginResult.NoSuchUser, "Peter", "123!##"}
};
// ForEachRow is my own extension method
testDataTable.ForEachRow((row) =>
{
var result = (LoginResult)row[0];
var username = (string)row[1];
var password = (string)row[2];
mock.Setup(o => o.Login(
It.Is<string>(u => u == username),
It.Is<string>(p => p == password)
)).Returns(result);
});
return mock.Object;
Code that I wish:
var mock = new Mock<ILogin>();
new object[,]
{
{ LoginResult.Success, "Jack", "123!##"}
, { LoginResult.WrongPassword, "Jack", "123321"}
, { LoginResult.NoSuchUser, "Peter", "123!##"}
}.ForEachRow((row) =>
{
var exprTree = (ILogin o)=>o.Login("ANY", "ANY");
AutoSetup(mock, exprTree, row); // <---- How to write this AutoSetup?
});
return mock.Object;
How to write the AutoSetup(mock, exprTree, dataArray) function above?
It takes three parameters:
mock: A mock object, e.g. new Mock()
exprTree: Expression tree that represents a method to be setup
dataArray: An object[], the 0 element is the expected result, and others are parameters that passed to the method

Answer 1

This was an interesting challenge. I think I have a working implementation for your AutoSetup method, using the expressions API. If anyone has a simpler solution, I'd love to see it.
static void AutoSetup<TMock, TResult>(Mock<TMock> mock, Expression<Func<TMock, TResult>> exprTree, object[] items) where TMock : class
{
var methodCallExpr = exprTree.Body as MethodCallExpression;
var arguments = items.Skip(1).Select(o => Expression.Constant(o));
var updatedMethod = methodCallExpr.Update(methodCallExpr.Object, arguments);
var updatedLambda = exprTree.Update(updatedMethod, exprTree.Parameters);
mock.Setup(updatedLambda).Returns((TResult)items[0]);
}
Here is a full working test as a console app, with an implementation of ForEachRow, which you didn't provide.
class Program
{
static void Main(string[] args)
{
var login = SetUp();
Console.WriteLine(login.Login("Jack", "123!##"));
Console.WriteLine(login.Login("Jack", "123321"));
Console.WriteLine(login.Login("Peter", "123!##"));
Console.ReadKey();
}
static ILogin SetUp()
{
var mock = new Mock<ILogin>(MockBehavior.Strict);
var rows = new object[,]
{
{ LoginResult.Success, "Jack", "123!##" },
{ LoginResult.WrongPassword, "Jack", "123321" },
{ LoginResult.NoSuchUser, "Peter", "123!##" }
};
rows.ForEachRow((row) => AutoSetup(mock, (ILogin l) => l.Login("ANY", "ANY"), row));
return mock.Object;
}
private static void AutoSetup<TMock, TResult>(Mock<TMock> mock, Expression<Func<TMock, TResult>> exprTree, object[] items) where TMock : class
{
var methodCallExpr = exprTree.Body as MethodCallExpression;
var arguments = items.Skip(1).Select(o => Expression.Constant(o));
var updatedMethod = methodCallExpr.Update(methodCallExpr.Object, arguments);
var updatedLambda = exprTree.Update(updatedMethod, exprTree.Parameters);
mock.Setup(updatedLambda).Returns((TResult)items[0]);
}
}
public static class ArrayExtensions
{
public static void ForEachRow<T>(this T[,] rows, Action<T[]> action)
{
var x = rows.GetLength(1);
var y = rows.GetLength(0);
for (int i = 0; i < y; i++)
{
var row = new T[x];
for (int j = 0; j < x; j++)
{
row[j] = rows[i, j];
}
action(row);
}
}
}
public interface ILogin
{
LoginResult Login(string p1, string p2);
}
public enum LoginResult
{
Success,
WrongPassword,
NoSuchUser
}
EDIT: You asked in a comment about how to take advantage of the variable parameter matching that Moq provides with the It.IsAny<> method. Because what you pass to your Mock.Setup() is an expression tree, it's able to scan the method parameters and implement special behaviour for any that are calls to It.IsAny<>. However, if you use It.IsAny<> in your test data array, by the time we retrieve it from your items array to set in on the expression, it's not a method call but simply the result of the call it It.IsAny<> which is default(T) (see here).
We need some way of specifying in your test data array that the parameter should be any. Then we can check for this special case and generate the correct MethodCallExpression representing a call to It.IsAny<>.
Here are the changes I made to support this:
Add an Any type to use in your test data
public class Any<T>
{
private Any() { }
public static Any<T> Param { get { return new Any<T>(); } }
}
Update the AutoSetup method to handle this special case:
private static void AutoSetup<TMock, TResult>(Mock<TMock> mock, Expression<Func<TMock, TResult>> exprTree, object[] items) where TMock : class
{
var arguments = items.Skip(1).Select(o => {
var type = o.GetType();
if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(Any<>))
{
var typeParameter = type.GetGenericArguments();
var genericItIsAny = typeof(It).GetMethod("IsAny");
var itIsAny = genericItIsAny.MakeGenericMethod(typeParameter);
return Expression.Call(itIsAny) as Expression;
}
return Expression.Constant(o);
});
var methodCallExpr = exprTree.Body as MethodCallExpression;
var updatedMethod = methodCallExpr.Update(methodCallExpr.Object, arguments);
var updatedLambda = exprTree.Update(updatedMethod, exprTree.Parameters);
mock.Setup(updatedLambda).Returns((TResult)items[0]);
}
In the test data, use the Any type
{ LoginResult.Success, "NoPasswordUser", Any<string>.Param }
Depending on how you're storing your test data, you might need another way of identifying parameters that you want to be variable (specially formatted string?), but in general this should give you an idea about how to create the correct expressions.