Testing Abstract Class with a mock

AbstractWithAmock.cs

public class TestingAnAbstractClassWithAMock
{
    [Fact]
    public void Should_return_correct_message()
    {
        var mock = new Mock<MyAbstractClass>();
        var result = mock.Object.MyMethodOnAbstractClass("fish");
        Assert.Equal("I like fish in an abstract sense.", result);
    }
}

public class MyAbstractClass
{
    public string MyMethodOnAbstractClass(string input)
    {
        return "I like " + input + " in an abstract sense.";
    }
}