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How to write unit test for service having dependency on other service or database

Sorry if I am asking very basic question,
I have set of web services (developed using .Net WebApi). These services are either business layer or data access layer APIs. These APIs are either dependent on other services or database itself.
I want to write unit test cases for it. I have following questions
As business layer APIs has dependency on data access service or some other service. If I write unit test just to invoke business API then it would invoke data access API. Is this the correct way to write unit test case? or should I inject all dependency object with unit test? I think earlier one would be integration test not unit test.
Should I write unit tests for Data access layer at all? I checked this link (Writing tests for data access code: Unit tests are waste) and it says DAL does not require unit tests. Should I still write tests for data access layer. I think it would be integration test not unit tests?

Question 1:
I would say if you want to do TDD, then it's not the "correct" way, because as you said, you would be performing integration tests. Then again, maybe you don't want to do TDD and integration tests are good enough for you, but to answer the question: this wouldn't be the proper way to **unit-**test your code.
Question 2
I would say it depends what you have in your data access layer. For instance, if you implement repositories, you will probably want to write a few tests.
Save method
You want to make sure that given an entity that you have retrieved from your repository, editing some properties of this entity and persisting the changes will actually save the modifications and not create a new entity. Now: you might think this is an integration test, but it really depends on how well designed your code is. For instance, your repository could be just an extra layer of logic on top of a low-level ORM. In that case, when testing the save method, what you will do is that you will assert that the right methods are called with the right parameters on the ORM service injected in your repository.
Errors and exceptions
While accessing data, it is possible to have problems such as connection to the database being broken, or that the format of the data is not as expected, or deserialization problems. If you want to provide some good error handling and perhaps create custom exceptions and add more information to them depending on the context, then you definitely want to write tests to make sure the corrext information is propagated
on the other hand
If your DAL is just a few classes that wrap a non-mockable ORM, and you don't have any logic in there, then perhaps you don't need tests, but it seems that this doesn't happen too often, you will pretty much always have a bit of logic that can go wrong and that you want to test.

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!

Dependent (Procedural) Unit Testing in Visual Studio 2012

In an MVC4 C# website, we are using Unit Testing to test our code. What we are currently doing is creating a mock database, then testing each layer:
Test the Database - connecting, initializing, load, etc.
Test the code accessing the database
Test the view layer
I want these three categories to be run in order and only if the previous one passed. Is this the right way to go about it? The old way we were doing it was using a Dependency Injection framework was a weird approach to mock testing. We actually created a mock class for each data accessor, which sucks because we have to re implement the logic of each method, and it didn't really add any value because if we made a mistake with the logic the first time, we'll make it a second.

I want these three categories to be run in order and only if the
previous one passed. Is this the right way to go about it?
No. You should be test everything in isolation and because of that any failing data access code should be completely unrelated to the view. So the view unit tests should fail for a completely different reason and because of that you should always run all tests.
In general, tests should run in isolation, and should not depend on any other tests. It seems to me that the view layer still depends on the data access code, but that you only abstracted the layer below. In that case, from the view's perspective, you are mocking an indirect dependency, which makes your unit tests more complex than strictly needed.
The old way we were doing it was using a Dependency Injection
framework was a weird approach to mock testing
I'm not sure if I get this, but it seems as if you were using the DI container inside your unit tests. This is a absolute no-no. Don't clutter your tests with any DI framework. And there's no need to. Just design your classes around the dependency injection principle (expose all dependencies as constructor arguments) and in your test you just manually new up the class under test with fake dependencies -or- when this leads to repetitive code, create a factory method in your test class that creates a new instance of the class under test.
We actually created a mock class for each data accessor, which sucks
I'm not sure, but it sounds as if there's something wrong with your design here. You would normally have a IRepository<T> interface for which you would have multiple implementations, such as a UserRepository : IRepository<User>, and OrderRepository : IRepository<Order>. In your test suite, you will have one generic FakeRespository<T> or InMemoryRepository<T> and you're done. No need to mock many classes here.
Here are two great books you should definitely read:
The Art of Unit Testing
Dependency Injection in .NET
Those books will change your life. And since you'll be reading anyway, do read this book as well (not related to your question, but code be a life changer as well).

Unit testing the repository. NHibernate

I've got NHibernate-based (constructor ISessionFactory injection) generic repository implementation which is stored inside DAL. It implements contract which is stored in `Domain Layer'.
Should I test real repository behavior using SQl CE or should I refactor my application to support agnostic-like (like in Tim Maccharty's book http://www.wrox.com/WileyCDA/WroxTitle/productCd-0470147563,descCd-authorInfo.html) Unit of Work and then give my fake implementation of IUnitOfWorkRepository?
Is it a valid approach to run tests on a local database exposing real repository implementation?
Thanks!

The issue is what your are testing and why. That will answer the question.
If:
I want to test a third party tool
That is, are you testing if NHibernate is working (not a kind of test
I do). Then do whatever it requires, so refactoring not required. Loose yourself.
I want to test how my code interacts with a thrid party tool
Then you are talking about what I like to call a interaction test. Refactoring is required as your more interested in how your using NHiberate than if it works.
I want to test my code
The abstract NHibernate entirely. Do whatever is necessary ... wrapper? Your now back into unit testing.
I want to test my application from a user point of view
I think this is above the scope your talking. But you can use this scope talking about components. So ... hmmm ... worthwhile but not easy. Not a unit test, so you want to instantiate the component/app and run the whole thing as its 'user' does. I call these 'UATs' and usually implement as 'Coded UATs'.

A unit test is testing a unit in isolation. So, no, it's not even a unit test if you're going to the database.
Abstract away and test your repositories with mocked up interfaces.

I think to test the repositories you need to use the actual scenario. Otherwise you don't have any other place to test the database access. Mocking the repositories is not a good practice. Because you don't have any logic which is need to test in the repositories. I think you need to write integration tests which is calling actual repositories to have any benefit from it.

Unit Testing Database Methods

I am currently working on a c# project which makes use of an SQLite Database. For the project I am required to do unit testing but was told that unit testing shouldn't involve external files, like database files for the testing and instead the test should emulate the database.
If I have a function that tests if a something exists in a database how could this sort of method be tested with a unit testing.

in general it makes life easier if external files are avoided and everything is done in code. There are no rules which says "shouldn't", and sometimes it just makes more sense to have the external dependency. But only after you have considered how not to have it, and realized what the tradeoffs are.
Secondly, what Bryan said is a good option and the one I've used before.

In an application that uses a database, there will be at least one component whose responsibility is to communicate with that database. The unit test for that component could involve a mocked database, but it is perfectly valid (and often desirable) to test the component using a real database. After all, the component is supposed to encapsulate and broker communication with that database -- the unit test should test that. There are numerous strategies to perform such unit tests conveniently -- see the list of related SO questions in the sidebar for examples.
The general prescription to avoid accessing databases in unit tests applies to non-database components. Since non-database components typically outnumber database-related components by a wide margin, the vast majority of unit tests should not involve a database. Indeed, if such non-database components required a database to be tested effectively, there is likely a design problem present -- probably improper separation of concerns.
Thus, the principle that unit tests should avoid databases is generally true, but it is not an absolute rule. It is just a (strong) guideline that aids in structuring complex systems. Following the rule too rigidly makes it very difficult to adequately test "boundary" components that encapsulate external systems -- places in which bugs find it very easy to hide! So, the question that one should really be asking oneself when a unit test demands a database is this: is the component under test legitimately accessing the database directly or should it instead collaborate with another that has that responsibility?
This same reasoning applies to the use of external files and other resources in unit tests as well.

With SQLite, you could use an in-memory database. You can stage your database by inserting data and then run your tests against it.

Once databases get involved it always blurs the line between unit testing and integration testing. Having said that, it is always a nice and very useful test to be able to put something in a database (Setup), Do your test and remove it at the end (Cleanup). This lets you test end to end one part of your application.
Personally I like to do this in an attribute driven fashion. By Specifying the Sql scripts to run for each test as an attribute like so ..
[PreSqlExecute("SetupTestUserDetails.sql")]
[PostSqlExecute("CleanupTestUserDetails.sql")]
public void UpdateUserNameTest()
{
The connectionstrings come from the app.config as usual and can even be a symbolic link to the app.config in your main project.
Unfortunately this isn't a standard feature with the MS test runner that ships with visual studio. If you are using Postsharp as your AOP framework, this is easy to do. If not, you can still get the same functionality for standard MS Test Runner, by using a feature of .Net called "Context Bound Objects". This lets you inject custom code into an object creation chain to do AOP like stuff as long as your objects inherit from ContextBoundObject.
I did a blog post with more details and a small, complete code sample here.
http://www.chaitanyaonline.net/2011/09/25/improving-integration-tests-in-net-by-using-attributes-to-execute-sql-scripts/

I think is really bad idea to have unit tests that depends on database information.
Also I think is a bad idea to use sqlite for unit tests.
You need to test objects protocol, so if you need something in your tests you should create them somewhere in the tests (usually at setUp).
Since is difficult to remove persistence, the popular way to do it is using SQLite, but always create what you need in unit tests.
check this link Unit Tests And Databases this will be more helpful I think

It's best to use a mocking framework, to mimic a database. For C# there is the Entity Framework. Even the use of sqlite is an outside dependency to your code.