I am using some COM library in my C# which is bound to particular hardware and doesn't work without it. On development/testing computer I don't have that hardware. The method which is using library looks like this:
using HWSysManagerLib;
bool ProcessBias(HWSysManager systemManager, string hwPath)
{
int handle = systemManager.OpenConfiguration(hwPath);
...
// some magic goes here
// return result
}
The question is, can I mock HWSysManager for test method and how? There are few methods only in HWSysManager and it wouldn't be problem to simulate their functionality for test. A tiny example would be great on how to mock it, if it's possible at all.
You can use the adapter pattern here.
Create an interface named IHWSysManager
public interface IHWSysManager
{
int OpenConfiguration(string hwPath);
}
The real implementation class just delegates the work to the library:
public class HWSysManagerImpl : IHWSysManager
{
private HWSysManager _hwSysManager; //Initialize from constructor
public int OpenConfiguration(string hwPath)
{
return _hwSysManager.openConfiguration(hwPath);
}
}
Use the interface in your code like this:
bool ProcessBias(IHWSysManager systemManager, string hwPath)
{
int handle = systemManager.OpenConfiguration(hwPath);
...
// some magic goes here
// return result
}
Now you can mock your IHWSysManager interface with mock frameworks or you can create a stub class yourself.
You can use Typemock Isolator for faking HWSysManager.
For your example, you can do the following:
var fakeManager = Isolate.Fake.Instance<HWSysManager>();
Isolate.WhenCalled(() => fakeManager.OpenConfiguration("")).WillReturn(0);
And then, you can pass this faked manager to ProcessBias(IHWSysManager systemManager, string hwPath) as an argument.
As you said, you can simulate a few methods from IHWSysManager. So, me advice is to set up the behavior of this manager's methods using DoInstead():
Isolate.WhenCalled(() => fakeManager.OpenConfiguration("")).DoInstead(
context =>
{
//Your simulation
});
You can look here for more information. I think, it can be really useful for you.
I suppose you should create HWSysManager(or some other name) class to your Mock cases, add there some wanted methods and then mock them. For example:
class HWSysManager
{
public virtual int ExampleReturnIntMethod(int a)
{
var someInt = 0;
return someInt;
}
and then setup:
public void TestMethod()
{
Mock<HWSysManager> hwSysManager = new Mock<HWSysManager>();
hwSysManager.Setup(x => x.ExampleReturnInMethod(It.IsAny<int> ())).Returns(10); //if parameter is any of int, return 10 in this case
}
Then to use your Mocked object just use the 'object' property:
var hwSysInstance = hwSysManager.Object;
var result = hwSysInstance.ExampleReturnInMethod(2); //result will be 10 in this case - as we have mocked
In case above your methods/properties have to be virtual.
You can use interfaces also, in your case:
public interface HwsysManager
{
int OpenConfiguration(string hwPath);
}
public void TestMethod()
{
Mock<HwsysManager> hwsysManager = new Mock<HwsysManager>();
hwsysManager.Setup(x => x.OpenConfiguration(It.IsAny<string>())).Returns(10);
}
All features of this Mock library are described here:
https://github.com/Moq/moq4/wiki/Quickstart
Related
I have a preexisting Interface...
public interface ISomeInterface
{
void SomeMethod();
}
and I've extended this intreface using a mixin...
public static class SomeInterfaceExtensions
{
public static void AnotherMethod(this ISomeInterface someInterface)
{
// Implementation here
}
}
I have a class thats calling this which I want to test...
public class Caller
{
private readonly ISomeInterface someInterface;
public Caller(ISomeInterface someInterface)
{
this.someInterface = someInterface;
}
public void Main()
{
someInterface.AnotherMethod();
}
}
and a test where I'd like to mock the interface and verify the call to the extension method...
[Test]
public void Main_BasicCall_CallsAnotherMethod()
{
// Arrange
var someInterfaceMock = new Mock<ISomeInterface>();
someInterfaceMock.Setup(x => x.AnotherMethod()).Verifiable();
var caller = new Caller(someInterfaceMock.Object);
// Act
caller.Main();
// Assert
someInterfaceMock.Verify();
}
Running this test however generates an exception...
System.ArgumentException: Invalid setup on a non-member method:
x => x.AnotherMethod()
My question is, is there a nice way to mock out the mixin call?
I have used a Wrapper to get around this problem. Create a wrapper object and pass your mocked method.
See Mocking Static Methods for Unit Testing by Paul Irwin, it has nice examples.
You can't "directly" mock static method (hence extension method) with mocking framework. You can try Moles (http://research.microsoft.com/en-us/projects/pex/downloads.aspx), a free tool from Microsoft that implements a different approach.
Here is the description of the tool:
Moles is a lightweight framework for test stubs and detours in .NET that is based on delegates.
Moles may be used to detour any .NET method, including non-virtual/static methods in sealed types.
You can use Moles with any testing framework (it's independent about that).
I found that I had to discover the inside of the extension method I was trying to mock the input for, and mock what was going on inside the extension.
I viewed using an extension as adding code directly to your method. This meant I needed to mock what happens inside the extension rather than the extension itself.
I like to use the wrapper (adapter pattern) when I am wrapping the object itself. I'm not sure I'd use that for wrapping an extension method, which is not part of the object.
I use an internal Lazy Injectable Property of either type Action, Func, Predicate, or delegate and allow for injecting (swapping out) the method during a unit test.
internal Func<IMyObject, string, object> DoWorkMethod
{
[ExcludeFromCodeCoverage]
get { return _DoWorkMethod ?? (_DoWorkMethod = (obj, val) => { return obj.DoWork(val); }); }
set { _DoWorkMethod = value; }
} private Func<IMyObject, string, object> _DoWorkMethod;
Then you call the Func instead of the actual method.
public object SomeFunction()
{
var val = "doesn't matter for this example";
return DoWorkMethod.Invoke(MyObjectProperty, val);
}
For a more complete example, check out http://www.rhyous.com/2016/08/11/unit-testing-calls-to-complex-extension-methods/
If you just want to make sure that the extension method was invoked, and you aren't trying to setup a return value, then you can check the Invocations property on the mocked object.
Like this:
var invocationsCount = mockedObject.Invocations.Count;
invocationsCount.Should().BeGreaterThan(0);
Reason why it is not possible to mock an extension method is already given in good answers. I am just trying to give another possible solution with this answer: Extract a protected, virtual method with the call to the extension method and create a setup for this method in the test class/method by using a proxy.
public class Foo
{
public void Method()
=> CallToStaticMethod();
protected virtual void CallToStaticMethod()
=> StaticClass.StaticMethod();
}
and test
[TestMethod]
public void MyTestMethod()
{
var expected = new Exception("container exception");
var proxy = new Mock<Foo>();
proxy.Protected().Setup("CallToStaticMethod").Throws(expected);
var actual = Assert.ThrowsException<Exception>(() => proxy.Object.Foo());
Assert.AreEqual(expected, actual);
}
In my case extension method is a method around some public method of my class. So I checked call of that internal method. That approach is similar to Alvis answer (above).
So if you are using Moq, and want to mock the result of an Extension method, then you can use SetupReturnsDefault<ReturnTypeOfExtensionMethod>(new ConcreteInstanceToReturn()) on the instance of the mock class that has the extension method you are trying to mock.
It is not perfect, but for unit testing purposes it works well.
I am trying to mock the ManagementObjectSearcher class and have created a IManagementInfo interface, so how can i cast the interface to the ManagementObjectSearcher class?
ManagementObjectSearcher s = new ManagementObjectSearcher();
IManagementInfo info = s as IManagementInfo;
this creates me a null info object
ManagementObjectSearcher s = new ManagementObjectSearcher();
IManagementInfo info =IManagementInfo(s);
this gives me run time error (cannot typecast)
You cannot do that. Do you want to do it so that you can write unit tests? If you are trying to mock a class that you have no control of, then you have to wrap it in another class.
public class MyManagementObjectSearcherWrapper : IManagementInfo
{
public void TheMethodToMock()
{
var searcher = new ManagementObjectSearcher();
// The code you want to mock goes here
}
}
And you run your code like this:
public void YourCode(IManagementInfo info)
{
info.TheMethodToMock();
}
Then YourCode() will take either your wrapper or the mocked object. You create your mock using the IManagementInfo interface.
It looks as if you are trying to wrap a 3rd party/system object in order to aid unit testing.
Say that your starting point is
public class Dependency {
public string Foo() {
return "foo"; // machine, system, time, something else, dependent result
}
public string Bar() {
return "bar";
}
}
public class MySimpleClass {
public string MyFunc() {
return new Dependency().Foo();
}
}
[TestMethod]
public void TestSimple() {
var client = new MySimpleClass();
Assert.AreEqual("foo", client.MyFunc());
}
We are creating the Dependency inside the call because we are considering the creation cost to be less important than holding on to an instance of the Dependency. This will be dependent upon the situation. We could as easily have created a Dependency in the ctor and stored a copy which we invoked each time. Either way, we have no control over the output which makes unit testing messy.
We need to create a proxy for it.
1. Define an interface for the members that we need
Most likely, we do not need to use all of the members of the wrappee so only include in the interface those about which we care.
public interface IDependencyProxy {
string Foo();
}
2. Create a Proxy Class
We then create a proxy class wrapping the dependency and implementing interface. Again, we can create at start or on a call by call basis.
public class DependencyProxy : IDependencyProxy {
public string Foo() {
return new Dependency.Foo();
}
}
3. Define our client code in terms of the interface
We modify our client code slightly to use the IDependencyProxy interface instead of the Dependency. There are a few ways of doing this. I generally use an internal ctor which takes the dependency chained from a public ctor. (Use [InternalsVisibleTo] to allow the unit tests to see it)
public class MyRevisedClass {
private readonly IDependencyProxy dependency;
public MyRevisedClass()
: this( new DependencyProxy()) {}
internal MyRevisedClass(IDependencyProxy dependency) {
this.dependency = dependency;
}
public string MyFunc() {
return dependency.Foo();
}
}
This allows us a default behaviour for the production code (invokes the System object) and allows us to mock out the results for unit testing.
[TestMethod]
public void TestRevisedDefault() {
var client = new MyRevisedClass();
Assert.AreEqual("foo", client.MyFunc());
}
[TestMethod]
public void TestRevisedWithMockedDependency() {
var dep = new Mock<IDependencyProxy>();
dep.Setup(mk => mk.Foo()).Returns("bar");
var client = new MyRevisedClass(dep.Object);
Assert.AreEqual("bar", client.MyFunc());
}
Scratching my head how to do this.
Suppose I had a concrete class Foo with 2 virtual methods, Execute() and GetFile(). Execute() will call GetFile. I want to make sure that when it does, GetFile() will throw a couple of different exceptions that Foo is supposed to handle gracefully in a testable manner.
For my unit tests, I am envisioning instantiating a DynamicProxy<Foo> from castle project where I intercept the GetFile() to throw the exception, and then invoke the DynamicProxy object's Execute() method, and test the results, but I can't see how to do this.
Is this possible/ practical? If so, what would the creation of the dynamic proxy object look like?
You don't need to handcode your own proxy because most the mocking frameworks support your scenario.
Here is an example using Moq (Moq will create a dynamic proxy internally for you):
public class SomeException : Exception { }
public class Foo
{
public virtual int Execute()
{
try
{
GetFiles();
}
catch (SomeException)
{
return 1;
}
return 0;
}
public virtual void GetFiles()
{
//...
}
}
[Test]
public void FooTest()
{
var fooUnderTest = new Mock<Foo>();
fooUnderTest.CallBase = true;
fooUnderTest.Setup(f => f.GetFiles()).Throws(new SomeException());
var result = fooUnderTest.Object.Execute();
Assert.AreEqual(1, result);
}
You just need to take care to set Callbase = true which will:
Invoke base class implementation if no expectation overrides the
member (a.k.a. "Partial Mocks" in Rhino Mocks): default is false.
I'd like to be able to test a class initialises correctly using Moq:
class ClassToTest
{
public ClassToTest()
{
Method1(#"C:\myfile.dat")
}
public virtual void Method1(string filename)
{
// mock this method
File.Create(filename);
}
}
I thought I'd be able to use the CallBase property to create a testable version of the class, then use .Setup() to ensure Method1() does not execute any code.
However, creating the Mock<ClassToTest>() doesn't call the constructor, and if it did it'd be too late to do the Setup()!
If this is impossible, what is the best way round the problem whilst ensuring that the constructor behaves correctly?
EDIT: To make it clearer, I've added a parameter to Method1() to take a filename and added some behaviour. The test I'd like to write would be a working version of the following:
[Test]
public void ClassToTest_ShouldCreateFileOnInitialisation()
{
var mockClass = new Mock<ClassToTest>() { CallBase = true };
mockClass.Setup(x => x.Method1(It.IsAny<string>());
mockClass.Verify(x => x.Method1(#"C:\myfile.dat"));
}
Way down inside of Moq.Mock (actually inside the CastleProxyFactory that Moq uses)
mockClass.Object
will call the constructor by way of Activator.CreateInstance()
So your test would look something like
[Test]
public void ClassToTest_ShouldCreateFileOnInitialisation()
{
Mock<ClassToTest> mockClass = new Mock<ClassToTest>();
mockClass.Setup(x => x.Method1(It.IsAny<string>());
var o = mockClass.Object;
mockClass.Verify(x => x.Method1(#"C:\myfile.dat"));
}
I have a preexisting Interface...
public interface ISomeInterface
{
void SomeMethod();
}
and I've extended this intreface using a mixin...
public static class SomeInterfaceExtensions
{
public static void AnotherMethod(this ISomeInterface someInterface)
{
// Implementation here
}
}
I have a class thats calling this which I want to test...
public class Caller
{
private readonly ISomeInterface someInterface;
public Caller(ISomeInterface someInterface)
{
this.someInterface = someInterface;
}
public void Main()
{
someInterface.AnotherMethod();
}
}
and a test where I'd like to mock the interface and verify the call to the extension method...
[Test]
public void Main_BasicCall_CallsAnotherMethod()
{
// Arrange
var someInterfaceMock = new Mock<ISomeInterface>();
someInterfaceMock.Setup(x => x.AnotherMethod()).Verifiable();
var caller = new Caller(someInterfaceMock.Object);
// Act
caller.Main();
// Assert
someInterfaceMock.Verify();
}
Running this test however generates an exception...
System.ArgumentException: Invalid setup on a non-member method:
x => x.AnotherMethod()
My question is, is there a nice way to mock out the mixin call?
I have used a Wrapper to get around this problem. Create a wrapper object and pass your mocked method.
See Mocking Static Methods for Unit Testing by Paul Irwin, it has nice examples.
You can't "directly" mock static method (hence extension method) with mocking framework. You can try Moles (http://research.microsoft.com/en-us/projects/pex/downloads.aspx), a free tool from Microsoft that implements a different approach.
Here is the description of the tool:
Moles is a lightweight framework for test stubs and detours in .NET that is based on delegates.
Moles may be used to detour any .NET method, including non-virtual/static methods in sealed types.
You can use Moles with any testing framework (it's independent about that).
I found that I had to discover the inside of the extension method I was trying to mock the input for, and mock what was going on inside the extension.
I viewed using an extension as adding code directly to your method. This meant I needed to mock what happens inside the extension rather than the extension itself.
If you just want to make sure that the extension method was invoked, and you aren't trying to setup a return value, then you can check the Invocations property on the mocked object.
Like this:
var invocationsCount = mockedObject.Invocations.Count;
invocationsCount.Should().BeGreaterThan(0);
I like to use the wrapper (adapter pattern) when I am wrapping the object itself. I'm not sure I'd use that for wrapping an extension method, which is not part of the object.
I use an internal Lazy Injectable Property of either type Action, Func, Predicate, or delegate and allow for injecting (swapping out) the method during a unit test.
internal Func<IMyObject, string, object> DoWorkMethod
{
[ExcludeFromCodeCoverage]
get { return _DoWorkMethod ?? (_DoWorkMethod = (obj, val) => { return obj.DoWork(val); }); }
set { _DoWorkMethod = value; }
} private Func<IMyObject, string, object> _DoWorkMethod;
Then you call the Func instead of the actual method.
public object SomeFunction()
{
var val = "doesn't matter for this example";
return DoWorkMethod.Invoke(MyObjectProperty, val);
}
For a more complete example, check out http://www.rhyous.com/2016/08/11/unit-testing-calls-to-complex-extension-methods/
Reason why it is not possible to mock an extension method is already given in good answers. I am just trying to give another possible solution with this answer: Extract a protected, virtual method with the call to the extension method and create a setup for this method in the test class/method by using a proxy.
public class Foo
{
public void Method()
=> CallToStaticMethod();
protected virtual void CallToStaticMethod()
=> StaticClass.StaticMethod();
}
and test
[TestMethod]
public void MyTestMethod()
{
var expected = new Exception("container exception");
var proxy = new Mock<Foo>();
proxy.Protected().Setup("CallToStaticMethod").Throws(expected);
var actual = Assert.ThrowsException<Exception>(() => proxy.Object.Foo());
Assert.AreEqual(expected, actual);
}
In my case extension method is a method around some public method of my class. So I checked call of that internal method. That approach is similar to Alvis answer (above).
So if you are using Moq, and want to mock the result of an Extension method, then you can use SetupReturnsDefault<ReturnTypeOfExtensionMethod>(new ConcreteInstanceToReturn()) on the instance of the mock class that has the extension method you are trying to mock.
It is not perfect, but for unit testing purposes it works well.