Moq an interface and setting up a mock - unit-testing

Question

I have an Interface to check vowel and to return a char as
public interface IVowChecker
{
bool VowCheck(char a);
char ReturnChar(int n);
Student GetStudentById(int n);
}
It's concrete class implementation
public class VowChecker:IVowChecker
{
public bool VowCheck(char a)
{
if (a == 'a' || a == 'A')
return true;
return false;
}
public char ReturnChar(int n)
{
return (char)n;
}
public Student GetStudentById(int n)
{
var list = new []
{
new Student{RollNo=1,Name="A"},
new Student{RollNo=2,Name="B"},
new Student{RollNo=3,Name="C"},
new Student{RollNo=4,Name="D"},
new Student{RollNo=5,Name="E"},
new Student{RollNo=6,Name="F"},
};
var student = from i in list
where i.RollNo == n
select i;
return student.FirstOrDefault();
}
}
And a service using this VowChecker
public class MyCharService
{
private readonly IVowChecker _checker;
public MyCharService(IVowChecker checker)
{
_checker = checker;
}
public bool CheckInput(char a)
{
return _checker.VowCheck(a);
}
public char ReturnChar(int a)
{
return _checker.ReturnChar(a);
}
public Student GetStudentById(int n)
{
return _checker.GetStudentById(n);
}
}
I am using Xunit testing framework for unit testing and Moq library.
My unit test code is
public class MyCharServiceShould
{
...
[Theory]
[InlineData(65)]
[InlineData(68)]
public void BeAbleToReturnChar(int n)
{
var service = new Mock<IVowChecker>();
service.Setup(i => i.ReturnChar(n)).Returns('A');
var obj = new MyCharService(service.Object);
var result = obj.ReturnChar(n);
}
[Theory]
[InlineData(2)]
public void BeAbleToRetrieveStudent(int n)
{
var service = new Mock<IVowChecker>();
service.Setup<Student>(i => i.GetStudentById(n)).Returns<Student>(f => (Student)f);
var ob = new MyCharService(service.Object);
var res = ob.GetStudentById(2);
Assert.Equal(res.Name, "B");
}
}
My Student class
public class Student
{
public int RollNo{ get; set; }
public string Name { get; set; }
}
I have used a debugger in the last line of my test and checked the values of both the tests. For the 1st test I am expecting 'A' as the result and for the 2nd test I am expecting 'D' as the result. But in both the cases I am getting 'A' as the result. Can anyone kindly help me out where I am missing out the concept. Thank you.

Answer 1

The problem is that the setup for ReturnChar
service.Setup(i => i.ReturnChar(n)).Returns('A');
says,
Whenever ReturnChar() is called, give an answer of 'A'
It ignores the input 'n' and just returns 'A'. If you want it to return a different character for each test you will need to tweak the setup.
Perhaps
mockService.Setup(mk => mk.ReturnChar(It.IsAny<int>())).Returns<int>(n => (char)n);
EDIT: Extension to show returning objects (and fixed syntax on previous answer)
public class Student
{
public int Id { get; set; }
public string Name { get; set; }
}
public interface IService
{
Student FindStudentById(int id);
}
[TestMethod]
public void FindStudents()
{
var students = new[]
{
new Student {Id = 1, Name = "Mon" },
new Student {Id = 2, Name = "Tue" },
new Student {Id = 3, Name = "Wed" },
new Student {Id = 4, Name = "Thu" },
};
var mockService = new Mock<IService>();
mockService.Setup(mk => mk.FindStudentById(It.IsAny<int>())).Returns<int>(id => students.First(s => s.Id == id));
Assert.AreEqual("Wed", mockService.Object.FindStudentById(3).Name);
}