I am working on .NET 4.0 using C# in Windows 7.
I want to test the communication between some methods using mock. The only problem is that I want to do it without implementing an interface. Is that possible?
I just read a lot of topics and some tutorials about mock objects, but all of them used to mock interfaces, and not the classes. I tried to use Rhino and Moq frameworks.
Simply mark any method you need to fake as virtual (and not private). Then you will be able to create a fake that can override the method.
If you use new Mock<Type> and you don't have a parameterless constructor then you can pass the parameters as the arguments of the above call as it takes a type of param Objects
Most mocking frameworks (Moq and RhinoMocks included) generate proxy classes as a substitute for your mocked class, and override the virtual methods with behavior that you define. Because of this, you can only mock interfaces, or virtual methods on concrete or abstract classes. Additionally, if you're mocking a concrete class, you almost always need to provide a parameterless constructor so that the mocking framework knows how to instantiate the class.
Why the aversion to creating interfaces in your code?
With MoQ, you can mock concrete classes:
var mocked = new Mock<MyConcreteClass>();
but this allows you to override virtual code (methods and properties).
I think it's better to create an interface for that class. And create a unit test using interface.
If it you don't have access to that class, you can create an adapter for that class.
For example:
public class RealClass
{
int DoSomething(string input)
{
// real implementation here
}
}
public interface IRealClassAdapter
{
int DoSomething(string input);
}
public class RealClassAdapter : IRealClassAdapter
{
readonly RealClass _realClass;
public RealClassAdapter() => _realClass = new RealClass();
int DoSomething(string input) => _realClass.DoSomething(input);
}
This way, you can easily create mock for your class using IRealClassAdapter.
Hope it works.
If you cannot change the class under test, then the only option I can suggest is using MS Fakes https://msdn.microsoft.com/en-us/library/hh549175.aspx.
However, MS Fakes works only in a few editions of Visual Studio.
The standard mocking frameworks are creating proxy classes. This is the reason why they are technically limited to interfaces and virtual methods.
If you want to mock 'normal' methods as well, you need a tool that works with instrumentation instead of proxy generation. E.g. MS Moles and Typemock can do that. But the former has a horrible 'API', and the latter is commercial.
If worse comes to worse, you can create an interface and adapter pair.
You would change all uses of ConcreteClass to use the interface instead, and always pass the adapter instead of the concrete class in production code.
The adapter implements the interface, so the mock can also implement the interface.
It's more scaffolding than just making a method virtual or just adding an interface, but if you don't have access to the source for the concrete class it can get you out of a bind.
It is a bit old question but nevertheless. There are powerful mocking frameworks these days that are capable of mocking concrete classes like JustMock and Typemock.
I faced something like that in one of the old and legacy projects that i worked in that not contains any interfaces or best practice and also it's too hard to enforce them build things again or refactoring the code due to the maturity of the project business, So in my UnitTest project i used to create a Wrapper over the classes that I want to mock and that wrapper implement interface which contains all my needed methods that I want to setup and work with, Now I can mock the wrapper instead of the real class.
For Example:
Service you want to test which not contains virtual methods or implement interface
public class ServiceA{
public void A(){}
public String B(){}
}
Wrapper to moq
public class ServiceAWrapper : IServiceAWrapper{
public void A(){}
public String B(){}
}
The Wrapper Interface
public interface IServiceAWrapper{
void A();
String B();
}
In the unit test you can now mock the wrapper:
public void A_Run_ChangeStateOfX()
{
var moq = new Mock<IServiceAWrapper>();
moq.Setup(...);
}
This might be not the best practice, but if your project rules force you in this way, do it. Also Put all your Wrappers inside your Unit Test project or Helper project specified only for the unit tests in order to not overload the project with unneeded wrappers or adaptors.
Update:
This answer from more than a year but in this year i faced a lot of similar scenarios with different solutions.
For example it's so easy to use Microsoft Fake Framework to create mocks, fakes and stubs and even test private and protected methods without any interfaces.
You can read: https://learn.microsoft.com/en-us/visualstudio/test/isolating-code-under-test-with-microsoft-fakes?view=vs-2017
Related
I've seen multiple answers regarding 'how to stub your classes so you can control what happens within the SUT'.
They say one thing:
Create an interface and inject that interface using dependency injection and create a stub using that same interface that you then inject into the SUT.
However, what I've learned in my previous working places:
If you unit test, you test all classes/functionality.
Does that mean that for every class that has a specific function-layout you have to create an interface?
That would mean the amount of classes/files would just about be twice as many.
As seen in the example below, is this 'the way to go' or am I missing something in my unit testing process?
As a note:
I am using VS2012 Express. That means no 'Faker' framework. I am using the 'standard' VS2012 unit testing framework.
As a very, very simple example, which allows me to stub each interface passed down to a SUT.
IFoo.cs
public interface IFoo
{
string GetName();
}
Foo.cs
public class Foo : IFoo
{
public string GetName()
{
return "logic goes here";
}
}
IBar.cs:
public interface IBar : IFoo
{
IFoo GetFoo();
}
Bar.cs:
public class Bar : IBar
{
public string GetName()
{
return "logic goes here";
}
public IFoo GetFoo()
{
return null; // some instance of IFoo
}
}
IBaz.cs:
public interface IBaz
{
IBar GetBar();
}
Baz.cs:
public class Baz
{
public IBar GetBar()
{
return null; // some instance of IBar
}
}
In my opinion, you should not create interfaces just for the purpose of unit testing. If you start adding code abstractions to please the tools, then they are not helping you to be more productive. The code you write should ideally serve a specific business purpose/need - either directly, or indirectly by making the code base easier to maintain or evolve.
Interfaces sometimes do this, but certainly not always. I find that providing interfaces for components is usually a good thing, but try to avoid using interfaces for internal classes (that is, code only used inside of the given project, regardless of whether the types are declared public or not). This is because a component (as in, a set of classes working together to solve some specific problem) represents a larger concept (such as a logger or a scheduler), which is something that I may feasibly want to replace or stub out when testing.
The solution (hat tip to Robert for being first in the comments) is to use a mocking framework to generate a compatible substitution type at run-time. Mocking frameworks then allow you to verify that the class being tested interacted correctly with the substituted dummy. Moq is as mentioned a snazzy choice. Rhino.Mocks and NMock are two other popular frameworks. Typemock Isolator hooks into the profiler and is among the more powerful options (allows you to substitute even non-virtual private members), but is a commercial tool.
It's no good making up rules for how much you should unit test. It depends on what you're developing and what your goals are - if correctness always trumps time-to-market and cost is not a factor then unit testing everything is great. Most people are not so lucky and will have to compromise to achieve a reasonable level of test coverage. How much you should test may also depend on overall skill level of the team, expected lifetime and reuse of the code being written, etc.
Yes and no. In order to stub dependency you need some sort of abstraction, but that's in majority because of how mocking frameworks work (not all, naturally).
Consider simple example. You test class A that takes dependencies to classes B and C. For unit tests of A to work, you need to mock B and C - you'll need IB and IC (or base classes /w virtual members). Do you need IA? No, at least not for this test. And unless A becomes dependency to some other class, abstracting it behind interface/base class is not required.
Abstraction is great as it helps you build losely coupled code. You should abstract your dependencies. However, in practice some classes need not to be abstracted as they serve top-level/end-of-hierarchy/root roles and are not used elsewhere.
Maybe from a purist perspective that is the right way to go, but the really important thing is to make sure that external dependencies (e.g. database, network access, etc), anything that is computationally expensive/time consuming, and anything that isn't fully deterministic is abstracted away and easy to replace in your unit tests.
From a testing perspective, there is no need to make an interface for every class in your code. You make an interface to hide concrete execution of external dependencies behind a layer of abstraction. So instead of having a class that requires a direct HTTP connection mixed in with your logic, you would isolate the connection code to a class, have it implement an interface that is a member of your class, and inject a mock in place pf that interface. That way, you can test your logic in isolation, free of dependency, and the only "untested" code is boilerplate HTTP connection code that can be tested through other means.
I'd go the virtual method route. Creating interfaces for every class you need to test gets really burdensome, especially when you need tools like Resharper for the "go to implementation" every time you'd like to see the definition of a method. And there's the overhead of managing and modifying both files any time a method signature is changed or a new property or method is added.
I have a method call that I am unit testing. Inside that method call it makes a call to a method that is going to throw an error because it is trying to talk to a device that will not be available when the unit test is running. Is there a way to avoid that internal method call from being called?
Environment: C# Visual Studio 2010 unit testing within IDE
If you're unit testing a class with external dependencies then you must isolate the external dependancies using an interface which is injected in.
interface IDevice
{
void Run();
}
interface IDeviceOperator
{
void Operate();
}
class DeviceOperator : IDeviceOperator
{
private readonly IDevice _device;
public DeviceOperator(IDevice device)
{
_device = device;
}
public void Operate()
{
_device.Run();
// test other stuff here
}
}
[TestFixture]
public class DeviceOperatorTests
{
[Test]
public void Test_DeviceOperator_Operate()
{
IDevice device = A.Fake<IDevice>(); // Using FakeItEasy 3rd party mocking framework syntax
DeviceOperator deviceOperator = new DeviceOperator(device);
deviceOperator.Operate();
}
}
When doing unit testing you have to create mocks or stubs for all your external dependencies. A framework that could help you with that is Moq (it is plenty of mock frameworks if you want to explore).
These mock or stubs are just facades providing necessary interactions and data to pass your tests.
We may be able to help you more if you provide more details about that unavailable device.
There's probably a better way, but once or twice I've been in this situation where a method calls another, complicated method, and put an optional parameter at the end of the method you're testing like
public void DoSomething(int number, bool skipMethod= false)
{
if(!skipMethod)
MethodThatWillBreak();
{
So that in the normal course of running, it'll be fine, but in your unit test you can do
DoSomething(2,true);
But really, it suggests that you need to do some refactoring of your code, because your unit test should only be hitting one "unit". If you can test the method without calling the MethodThatWillBreak then what is it doing there in the first place.
Check out Working Effectively with Legacy Code book by Michael Feathers - it have a lot of suggestions on dealing with code that does not have unit test yet.
Possible approaches covered in the book:
extract dependency in interface - ideal approach (see jamespconnor's answer)
use flag to bypass call (see Colm Prunty's answer)
extract that call into virtual method and override in derived class used in unit test
pass delegate (may be less impact than full interface/derivation)
Sample for deriving from the class:
public class WithComplexDependency
{
public void DoSomething()
{
// Extract original code into a virtual protected method
// dependency.MethodThatWillBreak();
CallMethodThatWillBreak();
}
virtual protected void CallMethodThatWillBreak()
{
dependency.MethodThatWillBreak();
}
}
in test code derive from the class and provide own implementation:
public class WithMockComplexDependency : WithComplexDependency
{
// may also need to add constructor to call original one.
override protected void CallMethodThatWillBreak()
{
// do whatever is needed for your test
}
}
...
WithComplexDependency testObject = new WithMockComplexDependency();
testObject.DoSomething(); // now does not call dependency.MethodThatWillBreak()
...
To unit test correctly you should decouple the comunication with the device from the class you want to test! Abstract the partetalking to the device in another class implementing an interface, inject the communication class in the ctor of the object under test, now you can inject a mock implementation from outside and avoid the errore,the mmock implementation can also log call made to it or respond in a predefined way easing test.
Read a out dependency injection and inversion of control
Typically you would extract external dependencies from the class you're testing and will swap them with fake ones in your unit test. You would isolate them and test the part that you're interested in. I recommend that you look into Inversion of Control as well as one of the many Mocking Frameworks (Moq, Rhino Mocks etc.)
You probably don't want to SKIP the external. Instead you want to isolate the external dependencies such as accessing external devices. There are many ways to do this
a. You can use a third part isolation framework such as Moq, or RhinoMock, etc
b. You can use Moles framework (since you are using VS2010) - replace a .NET method with a delegate
http://research.microsoft.com/en-us/projects/moles/
c. Paid isolation frameworks such as TypeMock.
d. Or simply hand written fake implementation which uses in interface and your test uses the Fake implementation.
I have a C# class which instantiates on its own a NetworkCommunicator class. I'd like to mock out the NetworkCommunicator class for my unit test, and replace it with a pretty simple stub.
But the NetworkCommunicator is never passed as a parameter. It's created by the class being tested.
In Ruby, this is easy to mock out. In Java, this is why you need Dependency Injection, which is too heavy for this project. Is there a simple way to mock this out in C#, perhaps using Moq or something similar?
You mentioned that DI is too heavyweight for this project, why not try some Truck Driver's DI, thus:
public interface IDependency
{
void DoSomeStuff();
}
public class ClassUnderTest
{
private IDependency _dependency;
public ClassUnderTest(IDependency dependency)
{
_dependency = dependency;
}
public ClassUnderTest() : this(new Dependency())
{}
public void ImportantStuff()
{
_dependency.DoSomeStuff();
}
}
Using this constructor chaining technique, you can now mock the IDependency all you want, without worrying about hooking up DI or IoC.
Create a "TestClass" that inherits from your class under test.
Override that parameter with a mocked instance
Create a property on the class under test that returns the new instance
public class ClassUnderTest {
public string MethodYouAreTesting(int someInput) {
var networkCommunicator = GetNetworkCommunicator();
// Do some stuff that I might want to test
return "foo";
}
public virtual NetworkCommunicator GetNetworkCommunicator {
return new NetworkCommunicator();
}
}
[TestFixture]
public class ClassUnderTestTests {
public void GivenSomeCondition_MethodYouAreTesting_ReturnsFooString() {
var classToTest = new TestClassUnderTest();
var result = classToTest.MethodYouAreTesting(1);
Assert.That(result, Is.EqualTo("foo");
}
}
public class TestClassUnderTest : ClassUnderTest {
public override GetNetworkCommunicator {
return MockedNetworkCommunicator;
}
}
I read of this technique this in the "Art of Unit Testing" and use it frequently when refactoring to full DI doesn't make sense or when the class I'm testing isn't something I can change.
Hope this helps.
You should refactor your code and pass dependencies in. You can also use typemock as easier to use alternative to fakes in Visual Studio 2012.
There's the built-in Fakes system, pretty well described at http://msdn.microsoft.com/en-us/library/hh549175.aspx
If that is too heavy-weight for your use case you might find the PrivateObject class more useful.
I have a C# class which instantiates on its own a NetworkCommunicator class.
As you noticed, this is a show stopper in C# when you want to mock this thing out. Solution is simple, and depends on context/purpose of the instantiated class:
inject it as a dependency if it's reusable component
provide it via factory if it's something that should be created every time when demand comes in
Either way, you'll need DI (factory from the second example is naturally injected too).
In Java, this is why you need Dependency Injection, which is too heavy for this project.
Is dependency injection too heavy? DI is design pattern, it's only too heavy when used when it's not really needed. Your question clearly shows you need it. Perhaps you meant that DI container is too heavy for your project? This might be true, as depending on project's complexity, you should choose appropriate way to apply DI.
I'd like to raise one more point to be aware of when applying solution like the one proposed in Greg Smith's answer. Essentially, your API ends up with constructors:
public TestedClass() : this(new Dependency()) ...
public TestedClass(IDependency) ...
As appealing as it might be at first glance, when long-term perspective is taken into account, several issues start to emerge:
does TestedClass must have IDependency or can it do fine without it?
what default (parameterless constructor) defaults to (implementation detail-level knowledge is required to use it properly)?
it creates tightly coupled components (TestedClass assembly will possibly have to reference other assembly - Dependency's assembly, even though it might not be relevant to it anyhow)
This is an anti-pattern going under different names, e.g. Bastard Injection. Of course, some of those problems might be mitigated (like making constructor protected/internal or having default implementation in the same assembly), but the anti-pattern and its long-term consequences remain. Also note that it's by no means more simple, faster or less code than regular DI.
You'll have to ask yourself what's less heavy - applying proper DI, or going you ways around with anti-patterns and/or 3rd party frameworks (MS Fakes).
How to test the behavior of the implementations of interface methods in (abstract) classes without having to copy the tests to each class?
I have (abstract) classes that implement multiple interfaces. I know how each interface should behave, and I define this in test methods so that I don't have to manually repeat these tests for each and every implementation of an interface.
I could create for each interface an abstract class with the tests, and have an abstract method CreateSUT() that creates a new instance of the concrete class. But then I'd have to create a new class with the same CreateSUT() implementation for each interface a class implements, as C# does not support multiple inheritance. Is there a better way to do this?
Also note that I also want to test interfaces implemented in abstract classes that have several non-abstract subclasses, complicating the matter slightly.
This question is not about whether I should unit test my interface implementations. Opinions differ and I've decided to do it because I know how the interface implementations are expected to behave (never returning a null value, returning a read-only collection, etc) and putting these tests together makes it much easier for me to test their implementations, however many there may be.
Well, I didn't understand why you need this, but you can write static helper class with tests for your interface. E.g.
public static class IFooTests
{
public static void ShouldDoSomething(this IFoo foo)
{
// Assert something
}
}
Later for every object that implements IFoo interface you can quickly create test methods:
[Test]
public void ShouldDoSomething()
{
Bar bar = new Bar(); // create and setup your concrete object
bar.ShouldDoSomething(); // call interface test extension
}
You could create a list to hold instances of all concrete implementations of your interface, then go through each element in that list and assert the invariant in your test.
Depending on your test framework, there should be a way to get actionable feedback when the test fails.
A quick search found me this for nUnit: http://www.nunit.org/index.php?p=testCaseSource&r=2.5.9
You can mock the abstract class with moq or make a interface that implements all your interfaces and then have your abstract class implement your newly created interface then mock the new interface.
If I have interface IFoo, and have several classes that implement it, what is the best/most elegant/cleverest way to test all those classes against the interface?
I'd like to reduce test code duplication, but still 'stay true' to the principles of Unit testing.
What would you consider best practice? I'm using NUnit, but I suppose examples from any Unit testing framework would be valid
If you have classes implement any one interface then they all need to implement the methods in that interface. In order to test these classes you need to create a unit test class for each of the classes.
Lets go with a smarter route instead; if your goal is to avoid code and test code duplication you might want to create an abstract class instead that handles the recurring code.
E.g. you have the following interface:
public interface IFoo {
public void CommonCode();
public void SpecificCode();
}
You might want to create an abstract class:
public abstract class AbstractFoo : IFoo {
public void CommonCode() {
SpecificCode();
}
public abstract void SpecificCode();
}
Testing that is easy; implement the abstract class in the test class either as an inner class:
[TestFixture]
public void TestClass {
private class TestFoo : AbstractFoo {
boolean hasCalledSpecificCode = false;
public void SpecificCode() {
hasCalledSpecificCode = true;
}
}
[Test]
public void testCommonCallsSpecificCode() {
TestFoo fooFighter = new TestFoo();
fooFighter.CommonCode();
Assert.That(fooFighter.hasCalledSpecificCode, Is.True());
}
}
...or let the test class extend the abstract class itself if that fits your fancy.
[TestFixture]
public void TestClass : AbstractFoo {
boolean hasCalledSpecificCode;
public void specificCode() {
hasCalledSpecificCode = true;
}
[Test]
public void testCommonCallsSpecificCode() {
AbstractFoo fooFighter = this;
hasCalledSpecificCode = false;
fooFighter.CommonCode();
Assert.That(fooFighter.hasCalledSpecificCode, Is.True());
}
}
Having an abstract class take care of common code that an interface implies gives a much cleaner code design.
I hope this makes sense to you.
As a side note, this is a common design pattern called the Template Method pattern. In the above example, the template method is the CommonCode method and SpecificCode is called a stub or a hook. The idea is that anyone can extend behavior without the need to know the behind the scenes stuff.
A lot of frameworks rely on this behavioral pattern, e.g. ASP.NET where you have to implement the hooks in a page or a user controls such as the generated Page_Load method which is called by the Load event, the template method calls the hooks behind the scenes. There are a lot more examples of this. Basically anything that you have to implement that is using the words "load", "init", or "render" is called by a template method.
I disagree with Jon Limjap when he says,
It is not a contract on either a.) how the method should be implemented and b.) what that method should be doing exactly (it only guarantees the return type), the two reasons that I glean would be your motive in wanting this kind of test.
There could be many parts of the contract not specified in the return type. A language-agnostic example:
public interface List {
// adds o and returns the list
public List add(Object o);
// removed the first occurrence of o and returns the list
public List remove(Object o);
}
Your unit tests on LinkedList, ArrayList, CircularlyLinkedList, and all the others should test not only that the lists themselves are returned, but also that they have been properly modified.
There was an earlier question on design-by-contract, which can help point you in the right direction on one way of DRYing up these tests.
If you don't want the overhead of contracts, I recommend test rigs, along the lines of what Spoike recommended:
abstract class BaseListTest {
abstract public List newListInstance();
public void testAddToList() {
// do some adding tests
}
public void testRemoveFromList() {
// do some removing tests
}
}
class ArrayListTest < BaseListTest {
List newListInstance() { new ArrayList(); }
public void arrayListSpecificTest1() {
// test something about ArrayLists beyond the List requirements
}
}
I don't think this is best practice.
The simple truth is that an interface is nothing more than a contract that a method is implemented. It is not a contract on either a.) how the method should be implemented and b.) what that method should be doing exactly (it only guarantees the return type), the two reasons that I glean would be your motive in wanting this kind of test.
If you really want to be in control of your method implementation, you have the option of:
Implementing it as a method in an abstract class, and inherit from that. You will still need to inherit it into a concrete class, but you are sure that unless it is explicitly overriden that method will do that correct thing.
In .NET 3.5/C# 3.0, implementing the method as an extension method referencing to the Interface
Example:
public static ReturnType MethodName (this IMyinterface myImplementation, SomeObject someParameter)
{
//method body goes here
}
Any implementation properly referencing to that extension method will emit precisely that extension method so you only need to test it once.
How about a hierarchy of [TestFixture]s classes? Put the common test code in the base test class and inherit it into child test classes..
When testing an interface or base class contract, I prefer to let the test framework automatically take care of finding all of the implementers. This lets you concentrate on the interface under test and be reasonably sure that all implementations will be tested, without having to do a lot of manual implementation.
For xUnit.net, I created a Type Resolver library to search for all implementations of a particular type (the xUnit.net extensions are just a thin wrapper over the Type Resolver functionality, so it can be adapted for use in other frameworks).
In MbUnit, you can use a CombinatorialTest with UsingImplementations attributes on the parameters.
For other frameworks, the base class pattern Spoike mentioned can be useful.
Beyond testing the basics of the interface, you should also test that each individual implementation follows its particular requirements.
I don't use NUnit but I have tested C++ interfaces. I would first test a TestFoo class which is a basic implementation of it to make sure the generic stuff works. Then you just need to test the stuff that is unique to each interface.