Unit test using dependency injection and mock objects without hitting Database - unit-testing

Question

I'm new to unit testing.Can anyone explain me about how to done unit testing without hitting Database.
And also i want to know that, Is dependency injection essential for unit testing?
If yes, explain me with a sample code. It will be helpful for me.
I had already created unit testing for login, which hits Database. But i want to test the same case for the login, without hitting database.
In this, i used Microsoft.VisualStudio.TestTools.UnitTesting.
Here is my code,
[TestMethod]
public void _01_LoginUser_01_Valid()
{
BLUser.User.UserDTO user = new BLUser.User.UserDTO();
user.UserName = "mohan";
user.UserPassword = "abc";
BLUser.Model.Fs_User result = BLUser.User.LoginUser(user);
Assert.AreEqual("mohan", result.UserName);
}
And my business logic is,
public static Fs_User LoginUser(UserDTO userDTO)
{
try
{
var context = new UserDBEntities();
{
var LoginUser = context.Fs_User.Where(u => u.UserName == userDTO.UserName && u.UserPassword == userDTO.UserPassword).SingleOrDefault();
if (LoginUser == null)
ValidationError.LoginException((int)ExceptionCodes.InvalidPassword);
return LoginUser;
}
}
catch (Exception ex)
{
throw ex;
}
}

Answer 1

See my answer here: Solid Principle examples anywhere?
If you look at the idea of depending on an interface for your data access, you'll see how you could supply a 'fake' implementation of that interface for testing that would not depend on a database.
Based on your example, you need to make something like the following changes:
public class LoginThing
{
private readonly IAmSomeContext context;
public LoginThing(IAmSomeContext context)
{
this.context = context;
}
public Fs_User LoginUser(UserDTO userDTO)
{
try
{
var LoginUser =
this.context.Fs_User
.SingleOrDefault(
u =>
u.UserName == userDTO.UserName
&& u.UserPassword == userDTO.UserPassword);
if (LoginUser == null)
ValidationError.LoginException((int)ExceptionCodes.InvalidPassword);
return LoginUser;
}
catch (Exception ex)
{
throw ex;
}
}
}
And then your test can become something like:
[TestMethod]
public void _01_LoginUser_01_Valid()
{
BLUser.User.UserDTO user = new BLUser.User.UserDTO();
user.UserName = "mohan";
user.UserPassword = "abc";
var fakeContext = CreateFakeContextWith(user);
var thingUnderTest = new LoginThing(fakeContext);
BLUser.Model.Fs_User result = thingUnderTest.LoginUser(user);
Assert.AreEqual("mohan", result.UserName);
}
Creating the fake context would look something like this, if you used NSubstitute:
private IAmSomeContext CreateFakeContextWith(BLUser.User.UserDTO user)
{
var fakeContext = Substitute.For<IFakeContext>();
fakeContext.Fs_User.Returns(new List(new[] {user}));
return fakeContext;
}
The syntax might not be exact, but you get the point...