Mocking issue: Can not instantiate proxy of class: Microsoft.AspNetCore.Identity.UserManager`

Question

I am trying to create a unit test using Moq which test Microsoft.AspNetCore.Identity user manager. I know that Moq is good for mocking interfaces, but UserManager does not have interface.

Here is my code:

Mock<UserManager<User>> userManagerMock = new Mock<UserManager<User>>();
// rest of my code ...

here is the error:

Castle.DynamicProxy.InvalidProxyConstructorArgumentsException : Can not instantiate proxy of class: Microsoft.AspNetCore.Identity.UserManager`1[[WebAPI.Core.Model.User, Core, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]. Could not find a parameterless constructor.

Answer 1

You can mock classes with Moq. You just need to create a new Mock with valid constructor parameters. In your case:

var userManagerMock = new Mock<UserManager<User>>(Mock.Of<IUserStore<User>>(), null, null, null, null, null, null, null, null);

When creating new mock for class, Moq uses one of the constructors of the class, in the UserManager class, there is a single constructor with 9 parameters:

UserManager<TUser>(IUserStore<TUser>, IOptions<IdentityOptions>, IPasswordHasher<TUser>, IEnumerable<IUserValidator<TUser>>, IEnumerable<IPasswordValidator<TUser>>, ILookupNormalizer, IdentityErrorDescriber, IServiceProvider, ILogger<UserManager<TUser>>)

The only parameter that is mandatory is the first one, all the others you can pass null value.

Now you can setup any virtual method or property.

Full example:

[TestMethod]
public void MockUserManager()
{
    // Arrange
    var userManagerMock = new Mock<UserManager<User>>(Mock.Of<IUserStore<User>>(), null, null, null, null, null, null, null, null);
    userManagerMock.Setup(x => x.CheckPasswordAsync(It.IsAny<User>(), It.IsAny<string>())).ReturnsAsync(true);

    // Act
    var res = userManagerMock.Object.CheckPasswordAsync(new User(), "123456").Result;

    // Assert
    Assert.IsTrue(res);
}

public class User
{
}