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Unit testing C# database dependent code

I would like to create unit tests for data dependent code. For example:
A user class that has the usual create, update & delete.
If I wanted to create a test for "user already exists" scenario, or and update or delete test. I would need to know that a specific user already exists in my database.
In such cases, what would be the best approach to have stand alone tests for these operations that can run in any order?

When you have dependencies like this think about whether you want to be Integration Testing as opposed to Unit Testing. If you do want to do Unit tests take a look at using Mock Data.
Integration Testing:
Tests how you code integrates with different parts of a system. This can be making sure your code connects to a database properly or has created a file on the filesystem. These tests are usually very straight-forward and do not have the same constraint of "being able to run in any order." However, they require a specific configuration in order to pass which means they do float well from developer to developer.
Unit Testing: Tests your code's ability to preform a function. For example "Does my function AddTwoNumbers(int one, int two) actually add two numbers?" Unit tests are to ensure any changes in code does not effect the expected results.
When getting into areas like "Does my code call the database any enter the result correctly?" you need to consider that unit tests are not meant to interact with the system. This is where we get into using "mock data." Mock classes and mock data take the place of an actual system to just ensure that your code "called out in the way we were expecting." The difficult part about this is it can be done but most of the .Net Framework classes do not provide the needed Interfaces in order to do it easily.
See the MSDN page on Tesing for more info. Also, consider this MSDN article on Mock Data.

Dependency between two unit tests in c#

Suppose that we have two unit tests that are dependent on each other. TestA depends on TestB. Now we want to change the code so when we run TestA, TestB will automatically be run.
[TestMethod]
public void TestA()
{
string id = "123456789";
NewUser user = new NewUser();
Boolean idCheck = user.checkID(id);
Assert.IsFalse(idCheck);
}
[TestMethod]
[HostType("ASP.NET")]
[UrlToTest("http://localhost:1776/Login.aspx")]
[AspNetDevelopmentServerHost("$(SolutionDir)\\project", "/")]
public void TestB()
{
Page page = _testContextInstance.RequestedPage;
Button button = page.FindControl("BNewUser") as Button;
PrivateObject po = new PrivateObject(page);
po.Invoke("BNewUser_Click", button, EventArgs.Empty);
Assert.IsFalse(page.Visible);
}

Unit tests should be F.I.R.S.T. Where I means isolated (not only from external resources, but from other tests also). TestB should have single reason to fail - if requirement which it verifies is not implemented. In your case it can fail if TestA was not run before, but requirement for TestB is implemented. So you never can tell real reason of test failure.
If you need some preconditions to be set before running TestB, then you should add this preconditions setting to Arrange part of TestB.
UPDATE: Reuse of Unit Test Artifacts. Allow Us to Dream article is just a dreaming of re-using unit tests for integration testing:
In theory it looks interesting. But in practice unit tests and integration tests are very different. First should be isolated latter are quite the reverse - they should use real dependencies and external resources. Lets imaging you will use some dependency injection framework to provide different implementations of dependencies to your SUT - mocked for unit-tests and real for integration tests. Sounds good. But it will make unit tests very hard to maintain - you will not know setup of mocked object in current test, because you are moving arrange part of test out of test to dependency injection framework. All unit tests will have only act and assert parts, which will have some value, but they will be really hard to understand and maintain.
Next part is even worth - how would you configure dependency injection framework to provide different setups of mocks for every different unit test? Also integration tests will require additional setup and tear-down steps which don't exist in separate unit-tests (you should clear and fill database etc). Also I can't even imagine how long it will take to run several thousands of integration tests which require real database, services and files. Unit tests use mocks, thus they are fast. Integration tests are slow.
As you can see, these types of tests are very different by their nature. So just don't try to mix them and use each one as it supposed to be used.

I think you may want to use a common initialization for your unit test. You can validate the initialization inside of TestB before you continue.
Take a look at
c# unit test with common code repeated
this may answer your question.
As a rule, I hold the opinion that unit tests should not have dependencies, if you find that you cannot separate the two sets of functionality, you may consider re-factoring it.
Tim

Should I test if my controller's Action method are calling the repository methods and generating the right view?

I'm new to testing and I just started testing my MVC application.
Currently I'm testing if my controller's action method are calling the right repository methods which in turn reads or writes the data from database.
What I'm also testing is if the return type of the action method is View, PartialView or RedirectToRoute, etc.
I've got some comments saying that testing if the controller's Action method is calling the right function in repository doesn't really make sense. Is it true?
What should I include in my Unit test for my MVC application, that uses Repository pattern as well.

It could make sense to check if you action call correct method on your repository but you'll need to mock it to avoid access to database. Unit tests should be isolated from external components.
Although it's not ideal, you could replace your "real" database by a lightweight in memory Sqlite to avoid mocking your database access in your tests.
I personally use Moq as mocking framework but it is plenty of mature mocking framework for .NET.
Take into account that testing if a method is called checks behavior instead of status. This make test more fragil as becomes dependent on internal implementation, but depending your scenario it could be perfeclty valid.

Unit testing is about testing a component's behavior in isolation, meaning that while testing a specific component, this component doesn't interract with any external component.
Usually, the way to do that is using mocks. All your dependencies must be mock so you can control them.
Testing if a method have been called is valid. If the logic is not on your tested component, then your job is done. Your component call a function and case x,y and z in another case. Behavior is fine? Thats good enough.
If you have difficulties testing because you have a database dependency, thats usually a design problem. Usually, this is solved by using an database abstraction in front of the database, who its only job is the make call and return value from the database. That abstraction can be mock and injected in your tested class. That way, you can even return pre-configured values to your tested class and continue the process.

This depends on different scenarios, for ex, In Controller, You have one Action
bool SaveEmployee(), which inside calls, service and then Database Layer to save. So testing whether Emp is actually saved in db does not make sense as it should be in another Unit Test for corresponding Database layer Function. Here, you just need to verify the status after it is successful, Failed, Duplicate or throws some Exception. You can simply Mock the function and return bool or string(like Success, as appropriate) and verify actual output with expected Output.

TDD: .NET following TDD principles, Mock / Not to Mock?

I am trying to following TDD and I have come across a small issue. I wrote a Test to insert a new user into a database. The Insert new user is called on the MyService class, so I went ahead and created mytest. It failed and I started to implement my CreateUser method on my MyService Class.
The problem I am coming across is the MyService will call to a repository (another class) to do the database insertion.
So I figured I would use a mocking framework to mock out this Repository class, but is this the correct way to go?
This would mean I would have to change my test to actually create a mock for my User Repository. But is this recommended? I wrote my test initially and made it fail and now I realize I need a repository and need to mock it out, so I am having to change my test to cater for the mocked object. Smells a bit?
I would love some feedback here.
If this is the way to go then when would I create the actual User Repository? Would this need its own test?
Or should I just forget about mocking anything? But then this would be classed as an integration test rather than a unit test, as I would be testing the MyService and User Repository together as one unit.
I a little lost; I want to start out the correct way.

So I figured I would use a mocking framework to mock out this
Repository class, but is this the correct way to go?
Yes, this is a completely correct way to go, because you should test your classes in isolation. I.e. by mocking all dependencies. Otherwise you can't tell whether your class fails or some of its dependencies.
I wrote my test initially and made it fail and now I realize I need a
repository and need to mock it out, so I am having to change my test
to cater for the mocked object. Smells a bit?
Extracting classes, reorganizing methods, etc is a refactoring. And tests are here to help you with refactoring, to remove fear of change. It's completely normal to change your tests if implementation changes. I believe you didn't think that you could create perfect code from your first try and never change it again?
If this is the way to go then when would I create the actual User
Repository? Would this need its own test?
You will create a real repository in your application. And you can write tests for this repository (i.e. check if it correctly calls the underlying data access provider, which should be mocked). But such tests usually are very time-consuming and brittle. So, it's better to write some acceptance tests, which exercise the whole application with real repositories.
Or should I just forget about mocking anything?
Just the opposite - you should use mocks to test classes in isolation. If mocking requires lots of work (data access, ui) then don't mock such resources and use real objects in integration or acceptance tests.

You would most certainly mock out the dependency to the database, and then assert on your service calling the expected method on your mock. I commend you for trying to follow best practices, and encourage you to stay on this path.
As you have now realized, as you go along you will start adding new dependencies to the classes you write.
I would strongly advise you to satisfy these dependencies externally, as in create an interface IUserRepository, so you can mock it out, and pass an IUserRepository into the constructor of your service.
You would then store this in an instance variable and call the methods (i.e. _userRepository.StoreUser(user)) you need on it.
The advantage of that is, that it is very easy to satisfy these dependencies from your test classes, and that you can worry about instantiating of your objects, and your lifecycle management as a separate concern.
tl;dr: create a mock!

I have two set of testing libraries. One for UnitTests where I mock stuff. I only test units there. So if I would have a method of AddUser in the service I would create all the mocks I need to be able to test the code in that specific method.
This gives me a possibility to test some code paths that I would not be able to verify otherwise.
Another test library is for Integration tests or functional tests or whatever you want to call it. This one is making sure that a specific use case. E.g. Creating a tag from the webpage will do what i expect it to do. For this I use the sql server that shipps with Visual studio 2012 and after every test I delete the database and start over.
In my case I would say that the integration tests are much more important then the unit tests. This is because my application does not have so much logic, instead it is displaying data from the database in different ways.

Your initial test was incomplete, that's all. The final test is always going to have to deal with the fact the new user gets persisted.
TDD does not prescribe the kind of test you should create. You have to choose beforehand if it's going to be a unit test or some kind of integration test. If it's a unit test, then the use of mocking is practically inevitable (except when the tested unit has no dependencies to isolate from). If it's an integration test, then actual database access (in this case) would have to be taken into account in the test.
Either kind of test is correct. Common wisdom is that a larger unit test suite is created, testing units in isolation, while a separate but smaller test suite exercises whole use case scenarios.

Summary
I am a huge fan of Eiffel, but while the tools of Eiffel like Design-by-Contract can help significantly with the Mock-or-not-to-Mock question, the answer to the question has a huge management-decision component to it.
Detail
So—this is me thinking out loud as I ponder a common question. When contemplating TDD, there is a lot of twisting and turning on the matter of mock objects.
To Mock or Not to Mock
Is that the only binary question? Is it not more nuanced than that? Can mocks be approached with a strategy?
If your routine call on an object under test needs only base-types (i.e. STRING, BOOLEAN, REAL, INTEGER, etcetera) then you don't need a mock object anyhow. So, don't be worried.
If your routine call on an object under test either has arguments or attributes that require mock objects to be created before testing can begin then—that is where the trouble begins, right?
What sources do we have for constructing mocks?
Simple creation with:
make or default create
make with hand-coded base-type arguments
Complex creation with:
make with database-supplied arguments
make with other mock objects (start this process again)
Object factories
Production code based factories
Test code based factories
Data-repo based data (vs hand-coded)
Gleaned
Objects from prior bugs/errors
THE CHALLENGE:
Keeping the non-production test-code bloat to a bare minimum. I think this means asking hard but relevant questions before willy-nilly code writing begins.
Our optimal goal is:
No mocks needed. Strive for this above all.
Simple mock creation with no arguments.
Simple mock creation with base-type arguments.
Simple mock creation with DB-repo sourced base-type arguments.
Complex mock creation using production code object factories.
Complex mock creation using test-code object factories.
Objects with captured states from prior bugs/errors.
Each of these presents a challenge. As stated—one of the primary goals is to always keep the test code as small as possible and reuse production code as much as possible.
Moreover—perhaps there is a good rule of thumb: Do not write a test when you can write a contract. You might be able to side-step the need to write a mock if you just write good solid contract coverage!
EXAMPLE:
At the following link you will find both an object class and a related test class:
Class: https://github.com/ljr1981/stack_overflow_answers/blob/main/src/so_17302338/so_17302338.e
Test: https://github.com/ljr1981/stack_overflow_answers/blob/main/testing/so_17302338/so_17302338_test_set.e
If you start by looking at the test code, the first thing to note is how simple the tests are. All I am really doing is spinning up an instance of the class as an object. There are no "test assertions" because all of the "testing" is handled by DbC contracts in the class code. Pay special attention to the class invariant. The class invariant is either impossible with common TDD facilities, or nearly impossible. This includes the "implies" Boolean keyword as well.
Now—look at the class code. Notice first that Eiffel has the capacity to define multiple creation procedures (i.e. "init") without the need for a traffic-cop switch or pattern-recognition on creation arguments. The names of the creation procedures tell the appropriate story of what each creation procedure does.
Each creation procedure also contains its own preconditions and post-conditions to help cement code-correctness without resorting to "writing-the-bloody-test-first" nonsense.
Conclusion
Mock code that is test-code and not production-code is what will get you into trouble if you get too much of it. The facility of Design-by-Contract allows you to greatly minimize the need for mocks and test code. Yes—in Eiffel you will still write test code, but because of how the language-spec, compiler, IDE, and test facilities work, you will end up writing less of it—if you use it thoughtfully and with some smarts!

Is it a test smell to mix in real implementation and mocks?

I have a consumer class responsible for consuming a string and deciding what to do with it. It can either parse and insert the parse data in a database or notify an administrator.
Below is my implementation.
public void Consume(string email)
{
if(_emailValidator.IsLocate(email))
{
var parsedLocate = _parser.Parse(email);
// Insert locate in database
}
else if(_emailValidator.IsGoodNightCall(email))
{
// Notify email notifying them that a locate email requires attention.
_notifier.Notify();
}
}
Below is my unit test.
// Arrange
var validator = new EmailValidator();
var parser = new Mock<IParser>();
var notifier = new Mock<INotifier>();
var consumer = new LocateConsumer(validator, parser.Object, notifier.Object);
var email = EmailLiterals.Locate;
// Act
consumer.Consume(email);
// Assert
parser.Verify(x => x.Parse(email), Times.Once());
Is it code smell to mix mocks and real implementation in unit tests? Also, how do always having to test whether method abc() always ran once? It doesn't seem right that once I add a new unit test every time I add a function inside my if block. Seems like if I continue adding to my Consume method I'm create a trap.
Thank you.

To be nitpicking, a unit test is an automated test that tests a unit in isolation. If you combine two or more units, it's not a unit test any more, it's an integration test.
However, depending on the type of units you integrate, having lots of that type of integration tests may be quite okay.
Krzysztof Kozmic recently wrote a blog post about this where he describes how Castle Windsor has very few unit tests, but lots of integration tests. AutoFixture also has a large share of those types of integration tests. I think the most important point is that as a general rule the integration must not cross library boundaries.
In any case you can view the actual implementation as an extreme end of the Test Double Continuum, so just as there are scenarios where it makes sense to use Stubs, Mocks, Spies, or Fakes, there are also scenarios where the actual implementation may make sense.
However, just keep in mind that you are no longer testing the unit in isolation, so you do introduce a coupling between the units that makes it more difficult to vary each independently.
To conclude, I still consider it a smell because it should always be an occasion to stop and think. However, a smell indicates no more than that, and sometimes, once you've thought it over, you can decide to move along.

I would say a strong yes. Unit testing should be free of dependencies among components.

> Is it a test smell to mix in real implementation and mocks?
This is an integration test (combining 2 or more modules) and not a unittest (test one module in isolation)
My answer is No: I think it is ok to have mocks in integration test.