Is there a generic way to use SetReturnsDefault in Moq

Question

I have a data access interface looking roughly like this:

public interface IDataRepository
{
    DatabaseResult<Customer> GetAllCustomers();
    DatabaseResult<Report> GetAllReports();
    DatabaseResult<Order> GetAllOrders();
    [..] (there are many methods like this)
}

DatabaseResult is a public class that is used to attach some metadata to the returned information.

When I mock this interface I want every single method (I probably have > 100) to return an instance of DatabaseResult<WhatEverType>. Currently I need to call SetReturnsDefault for each type, e.g.

    var mockDb = new Mock<IDataRepository>();
    mockDb.SetReturnsDefault(new DatabaseResult<Customer>());
    mockDb.SetReturnsDefault(new DatabaseResult<Report>());
    mockDb.SetReturnsDefault(new DatabaseResult<Order>());

Is there a way to just tell Moq that when the return type of a method is DatabaseResult<SomeType> then always return a new instance DatabaseResult<SomeType>, regardless of what SomeType is?

Or maybe, even more generically, there is a way to tell Moq to always return a new instance if the return type is class/record/struct? And for common generic collection interfaces like IEnumerable<T>, IList<T>, IDictionary<T>, etc., just return a random .NET type that implements the interface?

Answer 1

Actually there is already general solution to your problem.

You need to install two packages: AutoFixture and AutoFixture.AutoMoq.

Classes included there allows for automatic mocking of interfaces.

Please see example unit tests presenting how it can be used to autmatically mock all interface's methods:

public class GenericType<T>
{
    public T Value { get; set; }
}

public interface IInterface
{
    GenericType<int> GetInt();
    GenericType<string> GetString();
    GenericType<object> GetObject();
}

public class AutoFixtureTests
{
    [Fact]
    public void Test2()
    {
        // Arrange
        var fixture = new Fixture().Customize(new AutoMoqCustomization());
        var mock = fixture.Create<Mock<IInterface>>().Object;

        // Act & Assert
        Assert.NotNull(mock.GetInt());
        Assert.NotNull(mock.GetString());
        Assert.NotNull(mock.GetObject());
    }

    [Fact]
    public void Test()
    {
        // Arrange
        var fixture = new Fixture();
        var mock = fixture.Create<Mock<IInterface>>().Object;

        // Act & Assert
        Assert.Null(mock.GetInt());
        Assert.Null(mock.GetString());
        Assert.Null(mock.GetObject());
    }
}