I know it may sound like a silly question as I've heard many saying that you should only do unit testing for public function and indeed, visual basic.net in Visual studio IDE only allows me to do unit testing for public function.
However, I got a public function that is calling to many other private functions.
If I do unit testing for that public function, that would be too complicated. I only want to test each private function individually to make sure it works correctly first, before jumping to the parent public function.
One solution I've had in my mind is that I could change all private functions to public ones so that Visual Studio allows me to do unit testing for them. But it is annoying me as I don't want them to be public.
Is there any suggestions you could let me know please?
many thanks in advance.
N.T.C
If you really can't break the code out into separate classes, you could change all of the private functions to be protected and then create a private class within your test class that inherits from the class you're trying to test (this would be named as a fake or stub, hence my advice to make it private. You don't want code outside of the test class to interact with this). Within your inherited class, create public functions for each of the now protected functions that simply call through to the base and write your unit tests against those instead.
I apologize if this capability is not available in VB:
Create a sub-class of the class you want to test. Ensure that the sub-class has public interfaces to the private functions.
As for "only unit test public functions?" That's horse manure. You test what might fail. For instance, you might have a class with only one public function, and you want to refactor into a set of calls on private functions to decrease the complexity. If you have to refactor your solution for any reason (as one of the comments suggested), then the first step is to have all the pieces of the solution tested that you will have to change during the refactoring.
Related
I see in this answer that for Java you can set the visibility of a private method to "true" in a unit test in order to test the method. Is there something like this available for VBA, so that I can unit test private methods using RD-VBA?
If not, and I have a class that works out some logic in three private methods and give it back to a return value, am I doomed to only give a input value and test the return value, without being able to test the three private methods doing the heave lifting in between?
You shouldn't need to write tests for private methods, regardless of the language. You test your public API, what's private is implementation detail that isn't relevant.
If it is relevant and important enough to be tested on its own, then you should extract that private method to another class, and expose it as a public member of that class.
For example once I had a form and I wanted to limit user input in a textbox to numeric characters, and since I'm reusing that logic elsewhere then instead of treating it as an implementation detail of my form, I extracted a AsciiInputValidator class, and its public IsValidNumericValue method could be tested in every possible way as its own SUT.
Don't test private methods: the public ones invoke them anyway.
Unfortunately the Extract Class refactoring feature is not implemented as of this writing, so for now Rubberduck can't do this automatically for you... but it's definitely in-scope and if you're reading this and you're up for a bit of a C# metaprogramming challenge, go for it, pull requests are always welcome!
Can you add a public wrapper like
public sub testPrivateSub(param1,param2...)
PrivateSub(param1,param2....)
end sub
private sub PrivateSub(param1,param2....)
....
end sub
Let's say I have a public method as shown below:
public void startService(int intParam1, int intParam2, boolean booleanParam) {
setupService(intParam1, intParam2, booleanParam); // call private method to perform prerequisites
// perform remaining logic to start service here
}
This method has a call to a private method inside the same class which has the same interface as the public method which calls it. The public startService() method is the only consumer of the private setupService() method.
Would it have been a better idea to just get rid of the private setupService() method call and just replace it with setupService()'s implementation? In this case it appears there is some redundancy that may be unnecessary but I'd like to get some professional opinions. I've run into this several times in my career but usually looked the other way in fear of breaking something.
I've encountered this often too.
I ask myself:
Is the private function doing too many things that could be further broken up into functions? If so, then I would much rather get rid of the single private function and call the smaller functions from within the public function. This makes the code more readable because you can at once glance see what the public method is doing. This goes well towards making code self-documenting too.
Is there a possiblity of a future use-case where that single private function might be used again? If not, then it is not needed to be made private at the moment. However, it can get difficult in the future if a part of the code in your public function has to be used by other functions (more testing during the transition).
All in all, it comes down to having optimal modularity in your functions. If the private function cannot be further broken down into independent functions, then I would just get rid of it and put its code as is in the public method.
I have looked at other discussions about this topic (on StackOverflow) however the other questions seem to be language specific whereas this is not language specific and I'm considering no longer using private methods, classes, and modules.
I want to test my private methods, classes, and modules so that I can more easily locate bugs. To allow me to do this I'm considering no longer using private methods, classes, and modules for two reasons, (1) I see no reasonable way of testing a private method, class, or module without injecting test code or using some sort of "magic" and (2) to improve code reuse. Note that I'm not considering no longer using private variables and properties because data needs protecting and does not provide behaviour therefore it does not need to be public during testing.
As a lame example, if you're writing a module called OneOperations that has two public methods addOne and subtractOne, and two private methods add and subtract. If you were not allowing yourself to have private methods you would put the two private methods into another module (basicOperations) where they are public and import those methods inside the OneOperations module. From this you should now be able to write testing code for all the methods in both modules without injecting code. An advantage of this is that the methods add and subtract can now be used in other modules by importing the basicOperations module (2 - improving code reuse).
I have a feeling this a bad idea, but I lack the real world experience to justify not doing this, which is why I've posted this question on StackOverflow.
So, how do you test your private methods, classes, and modules? Is not writing private methods, modules, and classes a potential solution?
1) Like in many other answers on this topic, the main question is why would you want to test your private methods? The purpose of a class is to provide some functionality to its clients. If you have comprehensive unit tests that prove that the public interface of this class behaves correctly, why do you care what it's doing in its private methods?
2) Your idea of not having private methods at all seems like cutting your leg off. For small projects it may be possible to have every tiny behaviour well separated and tested. But for large projects it's an overkill. What matters, is the domain logic behaving correctly.
Consider for example a method:
public double getDistanceSquared(Point other)
{
return getDifferenceSquared(this.x, other.x)
+ getDifferenceSquared(this.y, other.y);
}
private double getDifferenceSquared(double v1, double v2)
{
return (v1 - v2)*(v1 - v2);
}
Ad1) Does it really make sense to unit test getDifferenceSquared method, if getDistanceSquared returns correct results for all test cases?
Ad2) Creating a separate class for calculating squared distance between doubles - in case there is only one place when it'll be used leads to a swarm of tiny classes, with millions of tests. Also, constructors of your domain classes will accept like 10 different interfaces for every tiny thing they're doing internally.
Maintaining all this is a lot of unnecessary work. Imagine that you would like to change the method of calculating the distance (maybe use some precomputed values). The behaviour of getDistanceSquared would not change. But you would have to change all of the tests of getDifferenceSquared even though you shouldn't have to care how is the distance being calculated, as long as it's calculated correctly.
Diving into minor details when it's not necessary makes you forgot what you're really doing - you lose the "big picture view". Value your time, and focus on important problems.
As a side note, also - the main concern of unit tests is not "locating bugs" as you suggest. They impose a clean design, provide an always up-to-date documentation of your code's behaviour and allow convenient refactoring giving you flexibility. Additionally they assure you that the code is working as you expect it to.
http://artofunittesting.com/definition-of-a-unit-test/
http://en.wikipedia.org/wiki/Unit_testing#Benefits
There is another way to look at this, which is how do you generate a private method?
If we are following the TDD process properly, then the first thing we write is the test. At this point the test should contain all of our code, e.g.
public void ShouldAddTwoNumbers()
{
(1 + 1).ShouldEqual(2);
}
Yes, that looks appalling. But consider what happens as we write is some more tests.
public void ShouldAddTwoMoreNumbers()
{
(2 + 2).ShouldEqual(4);
}
Now we have something to reactor, so it can become
public void ShouldAddTwoNumbers()
{
Add(1, 1).ShouldEqual(2);
}
public void ShouldAddTwoMoreNumbers()
{
Add(2, 2).ShouldEqual(4);
}
private int Add(int a, int b)
{
return a+b;
}
So now we have a private method that we can test inside our test class. It's only when you complete further refactoring to move the code out into your application, that the private becomes an issue. Most automated refactoring tools will offer you the option of changing the methods signature at this point, so that the private method is still accessible, because its not private.
(There is a fabulous exercise called TDD as if you mean it by Keith Braithwaite which I've just paraphrased above)
However, this isn't the end of our refactorings and development. One thing that we should be doing as we write and refactor our tests is to delete old tests, for example when functionality is duplicated. Another is to extract new methods so we don't repeat ourselves. Both of these can lead to scenarios where we have private methods back in the non-test code base.
So my advice is to be pragmatic, make the best decision you can for the code that you have in front of you. I wouldn't advise not creating private methods, but I would instead look at the factors that lead you to create them.
I have inherited a project that has no interfaces or abstract classes i.e. concrete classes only and I want to introduce unit testing. The classes contain lots of functions, which contain business logic and data logic; breaking every rule of SOLID (http://en.wikipedia.org/wiki/SOLID_%28object-oriented_design%29).
I had a thought. I was thinking about creating interfaces for each of the poorly designed classes, exposing all functions. Then at least I can Mock the classes.
I am relatively new to Unit Testing (I have experience with a project, which was very well developed using interfaces in the right places). Is it a good idea to do this i.e. create interfaces for all the concrete classes (exposing all the functions and sub routines), just for unit testing?
I have spent some time researching this but I have not found an answer.
If your project has no tests at all, before adding any unit tests I'd much rather create higher level tests (i.e acceptance, functional and/or integration tests).
When you have those tests in place you know that the system is behaving as it should and also that it has certain level of 'external' quality (meaning by this that the inputs and outputs of your program are the expected ones).
Once your high level tests are working, you could try to add unit tests to the classes that already exist.
I bet that you will find yourself in the need to refactor some of the existing classes if you want to be able to unit test them so you can use your high level tests as a safety net that will tell you if you've broken anything.
This is a tough thing to tackle. I think you are on the right track. You'll end up with some ugly code (such as creating header interfaces for each monolithic class), but that should just be an intermediate step.
I'd suggest investing in a copy of Working Effectively with Legacy Code. First you could start by reading this distillation.
In addition to Karl's options (which let you mock via interception), you could also use Microsoft Fakes & Stubs. But these tools will not encourage you to refactor the code to adhere to SOLID principles.
Yes, that is a good start, however, having interfaces is less of a priority than having dependencies injected. If all of your legacy classes gain interfaces, but hidden internally they are still all interdependent, the classes will still be no easier to test. For instance, let's say you had two classes that looked like this:
Public Class LegacyDataAccess
Public Function GetAllSales() As List(Of SaleDto)
' Do work with takes a long time to run against real DB
End Function
End Class
Public Class LegacyBusiness
Public Function GetTotalSales() As Integer
Dim dataAccess As New LegacyDataAccess()
Dim sales As List(Of SaleDto) = dataAccess.GetAllSales()
' Calculate total sales
End Function
End Class
I know what you're already saying... "I wish the legacy code was at least layered that well", but lets use that as an example of some legacy code which would be hard to test. The reason it's hard to test is because the code reaches out to the database and executes a time-consuming query on the database and then calculates the results from that. So, in order to test it in its current state, you would need to first write out a bunch of test data to the database, then run the code to see if it returns the correct results based on that inserted data. Having to write a test like that is problematic because:
It is a pain to write the code to setup the test
The test will be brittle because it depends on the outside database working properly and on it containing all the correct supporting data
The test will take too long to run
As you correctly observe, interfaces are very important to unit testing. So, as you recommend, lets add interfaces to see if it makes it any easier to test:
Public Interface ILegacyDataAccess
Function GetAllSales() As List(Of SaleDto)
End Interface
Public Interface ILegacyBusiness
Function GetTotalSales() As Integer
End Interface
Public Class LegacyDataAccess
Implements ILegacyDataAccess
Public Function GetAllSales() As List(Of SaleDto) _
Implements ILegacyDataAccess.GetAllSales
' Do work with takes a long time to run against real DB
End Function
End Class
Public Class LegacyBusiness
Implements ILegacyBusiness
Public Function GetTotalSales() As Integer _
Implements ILegacyBusiness.GetTotalSales
Dim dataAccess As New LegacyDataAccess()
Dim sales As List(Of SaleDto) = dataAccess.GetAllSales()
' Calculate total sales
End Function
End Class
So now we have the interfaces, but really, how does that make it any easier to test? Now we can easily create a mock data access object, which implements the same interface, but that's not really the core problem. The problem is, how do we get the business object to use that mock data access object instead of the real one? To do that, you need to take your refactoring to the next level by introducing dependency-injection. The real culprit is the New keyword in the following line of the business class:
Dim dataAccess As New LegacyDataAccess()
The business class clearly depends on the data access class, but currently it is hiding that fact. It's lying about it's dependencies. It's saying, come-on, it's easy, just call this method and I'll return the result--that's all it takes. When really, it takes a lot more than that. Now, let's say we stopped it from lying about it's dependencies and made it so it unabashedly stated them, like this:
Public Class LegacyBusiness
Implements ILegacyBusiness
Public Sub New(dataAccess As ILegacyDataAccess)
_dataAccess = dataAccess
End Sub
Private _dataAccess As ILegacyDataAccess
Public Function GetTotalSales() As Integer _
Implements ILegacyBusiness.GetTotalSales
Dim sales As List(Of SaleDto) = _dataAccess.GetAllSales()
' Calculate total sales
End Function
End Class
Now, as you can see, this class is much easier to test. Not only can we easily create a mock data access object, but now we can easily inject the mock data access object into the business object. Now we can create a mock which quickly and easily returns exactly the data we want it to return and then see if the business class returns the correct calculation--no database involved.
Unfortunately, while adding interfaces to existing classes is a breeze, refactoring them to use dependency-injection typically requires a lot more work. You will likely need to plan out which classes make the most sense to tackle first. You may need to create some intermediary old-school wrappers which work the way the code used to, so you don't break existing code while you are in the process of refactoring the code. It's not a quick and easy thing, but if you are patient and in it for the long-haul, it is possible to do it, and you will be glad you did.
I would recommend you go the interface route, but if you want to pay for a solution, then try one of these:
TypeMock
JustMock
Creating interfaces to test the classes is not a bad idea - the goal of unit testing is to exercise if the functions on a class are functioning as expected. Depending on the classes you are working with, this could be easier said than done - if there are a lot of dependencies on global states, etc. you will need to mock accordingly.
Given how valuable unit tests are, putting a bit of work into them (to a limit) will benefit you and developers you work with.
I prefer to create interfaces and classes as you need to test things and not all upfront.
Besides interfaces, you can use some techniques to test legacy code. The one I often use is "Extract And Override", where you extract some piece off "untestable" code inside other method and make it overridable. Them derive the class that you want to test and override the "untestable" method with some sensing code.
Using a mock framework will be as easy as adding keyword Overridable to the method and sets the returning using the mock framework.
You can find many techniques on the book "Working Effectively with Legacy Code".
One thing about existing code, is that sometimes it is better to write integration tests than unit tests. And after you have the behavior under test, you create unit tests.
Another tip is to start with modules/class that have less dependencies, that way, you become familiar with the code with less pain.
Let me know if you need an example about "extract and override" ;)
In my src, there exist a class which contains a method
public static boolean doExtensionsMatch(String s, String t) {
There is nothing wrong with it, except that there is no need for it to be public. It is used inside the class where it is declared.
It is public however, since some time ago, i felt this method needed to be tested directly and thus, private visibility did not work for me.
At this point:
I'd rather not throw away those tests. If i make the method private however, tests will become unusable.
I would rather for tests to remain in it's current src-test folder, thus maintaining separate locations for source and tests
So, you tell me, what should i do?
Should i change the method to private and delete the tests?
You test interface to prove that class behaves as it should.
So private methods don't need to be tested as long as they aren't accessible. And even more - you shouldn't care of how interface does its work, you should be fine with just the results.
You test the behaviour, not the implementation.
I would suggest using partial classes. If your test classes are partial classes of the class to be tested they will have access to all methods and variables whether or not they are public.