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Unit testing on code that uses the Database
I am just starting with unit testing and wondering how to unit test methods that are making actual changes to my database. Would the best way be to put them into transactions and then rollback, or are there better approaches to this?
If you want proper test coverage, you need two types of tests:
Unit-tests which mock all your actual data access. These tests will not acually write to the database, but test the behaviour of the class that does (which methods it calls on other dependencies, etc.)
System tests (or integration tests) which check that your database can be accessed and modified. I would considered two types of tests here: simple plain CRUD tests (create / read / update / delete) for each one of your model objects, and more complex system tests for your actual methods, and everything you deem interesting or valuable to test. Good practices here are to have each test starting from an empty (or "ready for the test") database, do its stuff, then check state of the database. Transactions / rollbacks are one good way to achieve this.
For unit testing you need to mock or stub the data access code, mostly you have repository interface and you can stub it by creating a concrete repository which stores data in memory, or you could mock it using dynamic mocking framework ..
For system or integration testing, you need to re-create the entire database before each test method in order to maintain a stable state before each test.
As per some of the previous answers if you want to test your data access code then you might want to think about mocks and a system/integration test strategy.
But, if you want to unit test your SQL objects (eg sprocs, views, constraints in tables etc) - then there are a number of database unit testing frameworks out there that might be of interest (including one that I have written).
Some implement tests within SQL, others within your code and use mbUnit/NUnit etc.
I have written a number of articles with examples on how I approach this - see http://dbtestunit.wordpress.com/
Other resources that might be of use:
http://www.simple-talk.com/sql/t-sql-programming/close-those-loopholes---testing-stored-procedures--/
http://tsqlt.org/articles/
The general approach is to have a way to mock you database actions. So that your unit tests are not reliant on the database being available or in a certain state. That said it also implies design that facilitates the isolation required to mock away your data layer. Unit test and how to do it well is a huge topic. Take a look on the googley for Mock Frameworks, and Dependency injection for a start.
If you are not developing an O/R mapper, there's no need to test database code. You don't want to test ADO.NET methods, right? Instead you want to verify that the ADO.NET methods are called with the right values.
Search Google for repository pattern. You will create an implementation of IRepository interface with CRUD methods and test/mock this.
If you want to test against a real database, this would be more of an integration then a unit test. Wrapping your tests in transaction could be an idea to keep your database in a consistent state.
We've done this in a base class and used the TestInitialize and TestCleanup functions to make sure this always happens.
But testing against a real database will certainly bring you into performance problems. So make sure from the beginning that you can swap your database access code with something that runs in memory. I don't now which database access code your targeting but design patterns like UnitOfWork and Repository can help you to isolate your database code and replace it with an in memory solution.
Related
I know my question looks like I am searching for some shortcut but actually I have searched a lot and couldn't find a resource to learn unit testing specially for business layer which involves data update in database.
I did get resources to learn writing unit test cases in nunit but they all were testing static data. I don't want to learn unit test writing as a beginner, I have the idea of writing unit tests in nunit, my main question is how do we test methods which involves data insert/update/delete in database? Do we actually insert data while testing? Do mocking play a role in it?
Please help me with any resource that covers specially this case.
Thanks!
If your business layer is written in C#, as your tag suggests, then mocking the database is the best practice. You use a mocking framework that allows you to control the data layer and write asserts that your business layer does the correct thing under controlled (mocked) responses. If you use this approach then your test will be isolated and execute very fast without any connection to the database (you should be able to execute thousands of unit test within a second.)
If your database contains a lot of business logic itself then you can unit test it in isolation, but I would not use nunit for that.
If you decide to include the database in you nunit C# business logic test then you will have to deal with connections to the database, and shared state between test. You will be in a much more complex setup and deal with more complex errors.
Here is a good resource to start with: https://www.amazon.com/Pragmatic-Unit-Testing-Nunit-Programmers/dp/0974514020
Some of the entities that are under test, cannot be directly created using the constructor, but only through a Domain service, because the use of a Repository is needed, may be for some validation that requires a hit in the DB (imagine a unique code validation).
In my tests I have two options:
Create an entity using the domain service that exposes the entity creation, this requires me to mock all the repository interfaces needed by that service and instruct the relevant ones to behave correctly for a successfull creation
Somehow use directly the entity constructor (I use c# so i can expose an internal constructor to the test assembly) and get the entity bypassing the service logic.
I'm not sure on which is the best approach,
the 1st is the one I prefer because it tests the public behaviour of the Domain model, since from an outside perspective the only way to create the entity is passing through the Domanin service. But this solution brings in al lot of "Arrange" code due to the mock configuration needed.
The 2nd one is more direct, it creates the object bypassing the service logic, but it's a sort of cheating on the Domain model, it assumes that the test code knows the internals of the Domain model and that's not a good point. But the code is a bit more readable.
I make use of Builders the create entities in tests, so the configuration code needed by the 1st approach would be isolated in the builder code, but I still want to know what would be the correct way.
Essentially you are asking what 'level' you should test at. Option 2 is very much a Unit Test, as it would test the code of a single class only. Option 1 is more of an Integration Test as it would test several components together.
I tend to prefer Option 2 for unit tests, for the following reasons:
Unit tests are simpler and more effective if they test a single class only. If you use the factory service to create the object under test, your test doesn't have direct control over how the object is constructed. The will lead to messy and tedious test code, such as mocking all the repository interfaces.
I will usually have, in a different part of my test code base, actual Integration Tests (or Acceptance Tests) which test the entire application from front to back via it's public interfaces (with external dependencies such as databases mocked/stubbed out). I would expect these tests to cover Option 1 from your question so I don't really need to repeat Option 1 in the unit test suite.
You may ask, what's the point of starting up my whole application just to test a couple of classes? The answer is quite simple - by sticking to only two levels of testing, your test code base will be clean, readable and easy to refactor. If your tests are very varied in terms of the 'level' that they test at (some test a single class, some a couple of classes together, some the whole application) then the test code just becomes hard to maintain.
Some caveats:
This advice is for if you are developing an "application" that will be deployed and run. If you are developing a "shared library" that will be distributed to other teams to use as they see fit, then you should test from all the public entry points to the library, regardless of the 'level'. (But I still wouldn't call these tests "unit tests" and would separate them in the code base.)
If you don't have the ability to write full integration tests, then I would use Option 1 and 2. Just be wary of the test code base becoming bloated.
One more point - test things together if they change for the same reason. The situation you don't want to end up in after choosing Option 1 is having to change your Entity tests every time you make a change to the factory/repository code. If the behavior of each Entity has not changed, then you shouldn't have to change the tests.
You could probably avoid that conundrum by not creating your entity through a domain service in the first place.
If you feel the need to validate something about an entity before creating it, you could probably see it as a domain invariant and have it enforced by an Aggregate. That aggregate root would expose a method to create the entity.
As soon as the invariant is guaranteed by the Aggregate in charge of spawning the new Entity, everything can be tested against concrete objects in memory since the aggregate should have all needed data inside itself to check the invariant - there is no resorting to an external Repository. You can set up the creator aggregate to be in an invariant breaking state or non-invariant-breaking state all in memory and exercise the test directly on the aggregate's CreateMyEntity method.
Don't Create Aggregate Roots by Udi Dahan is a good read on that approach - the basic idea is that entities and aggregate roots aren't just born out of nowhere.
I have runned into to the issue regarding unit test of dataprovider's. What are the best way to implement that.
One solution would be to insert something into the database and read it to make sure that it's as expected. And then removing it again. But this requires more coding.
The other solution is to have an extra database, which i could test against. This also requires alot of work to implement it.
What are the correct way to implement it?
As others have pointed out, what you are describing is called integration testing. Integration testing is something you should definitely do but it's good to understand the differences.
A unit test tests an individual piece of code without any dependencies. Dependencies are things like a database, file system or a web service but also other internal classes that are complex and require their own unit tests. Unit tests are made to run very fast. Especially when performing test driven development (TDD) you want your unit tests to execute in the order of milliseconds.
Integration tests are used to test how different components work together. If you have made sure through unit tests that your business logic is correct, your integration tests only have to make sure that all connections between different elements are in place. Integration tests can take a long time but you have fewer of them than unit tests.
I wrote a blog post on this some time ago that explains the differences and shows you ways to remove external dependencies while unit testing: Unit Testing, hell or heaven?.
Now regarding, your question. When running integration tests against a database you have a couple of options:
Use delta testing. This means that at the beginning of your test you record the current state of your database. For example, you store that are now 3 people in the people table. Then in your test you add one person and verify that there are now 4 people. in the database. This can be used quite effectively in simple scenarios. However, when your project grows more complex this is probably not the way to go.
Use a transaction around your unit tests. This is an easy way to make sure that your tests don't leave any data behind. Just start a new transaction (using the TransactionScope class in the .NET Framework) at the beginning of the test. As long as you don't complete the transaction, all changes will be rolled back automatically.
Use a new database for each test. Using localdb support in Visual Studio 2012 and higher, this can be done relatively fast.
I've chosen for the transaction scope a couple of times before and it worked quite well. One thing that's very important when writing integration tests like this is to make sure that your tests don't depend upon eachother. They need to run in whatever order the test runner decides on.
You should also make sure to avoid any 'magic numbers'. For example, maybe you know that your database contains 3 people so in your test you add one person and then assert that there are four in the database. For readers of your tests (which will be you in a couple of days, weeks or months) this is very hard to understand. Make sure that your tests are self explaining and that you don't depend on external state that's not obvious from the test.
You cannot unit test external dependencies like database connections. There is a good post here about why this is the case. In short: external dependencies should be tested, but that's integration tests, not unit tests.
Normally you do write intergration test when you call your database from code. If you want to write unittest, you should have a look at mocking frameworks.
I am creating an unit test, but there are many entities. So do I have to insert all entities at database manually or is there any better solution?
Are you looking for something like Moq? You use it to create a Mock objects and Queryable lists of objects so that you don't need to put fake data into your database to test.
Have a look at this link on how to get going on writing unit tests. The one thing I think that may help you in regard to your question:
Mock out all external services and state
Otherwise, behaviour in those external services overlaps multiple tests, and state data means that different unit tests can influence each other’s outcome.
You’ve definitely taken a wrong turn if you have to run your tests in a specific order, or if they only work when your database or network connection is active.
(By the way, sometimes your architecture might mean your code touches static variables during unit tests. Avoid this if you can, but if you can’t, at least make sure each test resets the relevant statics to a known state before it runs.)
I use a code generator (CodeSmith with .NetTiers template) to generate all the DAL code. I write unit tests for my code (business layer), and these tests are becoming pretty slow to run. The problem is that for each test, I reset the database to have a clean state. Also, as I do a lot of tests, it seems that the latency of the database operations sum up to a pretty bit delay.
All DB operations are performed through a DataRepository class that is generated by .NetTiers. Do you know if there is a way to generate (or code myself) a mock-DataRepository that would use in-memory storage instead of using the database ?
This way, I would be able to use this mock repository in my unit tests, speeding them a lot, without actually changing anything to my current code !
Take a look at Dependency injection (DI) and Inversion of Control containers (IOC). Essentially, you will create an interface that that a new mock DB object can implement, and then the DI framework will inject your mock DB when running tests, and the real DB when running you app.
There are numerous free and open source libraries that you could use to help you out. Since you are in C#, one of the new and up and coming DI libraries is Ninject. There are many others too. Check out this Wikipedia article for others and a high level description.
From the description of the issue, I think you are performing the Integration test because your test is making use of the Business and the DAL and live database.
For unit testing, you deal with one layer of code with all other dependencies either mocked or stubbed. With this approach, you unit tests will be really fast to execute on every incremental code changes.
There are various mocking frameworks that you can use like Rhino Mock, Moq, typemock to name a few. (In my project, I use Rhino mock to mock the DAL layer and unit test Business Layer in Isolation)
Harsha
Some of our unit tests use data fetched from XML's which were generated from a database to mock db access. DAL classes are replaced by mock ones because they are all stored in a DI container.
The generation of the xml's is custom code, if you find an open source solution for this then I'm happy to hear it.
Edit after Stefan's answer: I recall another team using SQL CE for their test database