Avi Levin edited this page Sep 12, 2016 · 21 revisions
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Moq is intended to be simple to use, strongly typed (no magic strings!, and therefore full compiler-verified and refactoring-friendly) and minimalistic (while still fully functional!).


using Moq;

// Assumptions:
public class Bar 
   // Bar implementation

public interface IFoo {
   bool DoSomething(string);
   string DoSomethingStringy(string);
   bool TryParse(string, out string);
   bool Submit(ref Bar);
   int GetCount();
   int GetCountThing();

var mock = new Mock<IFoo>();
mock.Setup(foo => foo.DoSomething("ping")).Returns(true);

// out arguments
var outString = "ack";
// TryParse will return true, and the out argument will return "ack", lazy evaluated
mock.Setup(foo => foo.TryParse("ping", out outString)).Returns(true);

// ref arguments
var instance = new Bar();
// Only matches if the ref argument to the invocation is the same instance
mock.Setup(foo => foo.Submit(ref instance)).Returns(true);

// access invocation arguments when returning a value
mock.Setup(x => x.DoSomethingStringy(It.IsAny<string>()))
        .Returns((string s) => s.ToLower());
// Multiple parameters overloads available

// throwing when invoked with specific parameters
mock.Setup(foo => foo.DoSomething("reset")).Throws<InvalidOperationException>();
mock.Setup(foo => foo.DoSomething("")).Throws(new ArgumentException("command"));

// lazy evaluating return value
mock.Setup(foo => foo.GetCount()).Returns(() => count);

// returning different values on each invocation
var mock = new Mock<IFoo>();
var calls = 0;
mock.Setup(foo => foo.GetCountThing())
    .Returns(() => calls)
    .Callback(() => calls++);
// returns 0 on first invocation, 1 on the next, and so on

Matching Arguments

// any value
mock.Setup(foo => foo.DoSomething(It.IsAny<string>())).Returns(true);

// matching Func<int>, lazy evaluated
mock.Setup(foo => foo.Add(It.Is<int>(i => i % 2 == 0))).Returns(true); 

// matching ranges
mock.Setup(foo => foo.Add(It.IsInRange<int>(0, 10, Range.Inclusive))).Returns(true); 

// matching regex
mock.Setup(x => x.DoSomething(It.IsRegex("[a-d]+", RegexOptions.IgnoreCase))).Returns("foo");


mock.Setup(foo => foo.Name).Returns("bar");

// auto-mocking hierarchies (a.k.a. recursive mocks)
mock.Setup(foo => foo.Bar.Baz.Name).Returns("baz");

// expects an invocation to set the value to "foo"
mock.SetupSet(foo => foo.Name = "foo");

// or verify the setter directly
mock.VerifySet(foo => foo.Name = "foo");
  • Setup a property so that it will automatically start tracking its value (also known as Stub):
// start "tracking" sets/gets to this property
mock.SetupProperty(f => f.Name);

// alternatively, provide a default value for the stubbed property
mock.SetupProperty(f => f.Name, "foo");

// Now you can do:

IFoo foo = mock.Object;
// Initial value was stored
Assert.Equal("foo", foo.Name);

// New value set which changes the initial value
foo.Name = "bar";
Assert.Equal("bar", foo.Name);
  • Stub all properties on a mock (not available on Silverlight):


// Raising an event on the mock
mock.Raise(m => m.FooEvent += null, new FooEventArgs(fooValue));

// Raising an event on a descendant down the hierarchy
mock.Raise(m => m.Child.First.FooEvent += null, new FooEventArgs(fooValue));

// Causing an event to raise automatically when Submit is invoked
mock.Setup(foo => foo.Submit()).Raises(f => f.Sent += null, EventArgs.Empty);
// The raised event would trigger behavior on the object under test, which 
// you would make assertions about later (how its state changed as a consequence, typically)

// Raising a custom event which does not adhere to the EventHandler pattern
public delegate void MyEventHandler(int i, bool b);
public interface IFoo
  event MyEventHandler MyEvent; 

var mock = new Mock<IFoo>();
// Raise passing the custom arguments expected by the event delegate
mock.Raise(foo => foo.MyEvent += null, 25, true);


var mock = new Mock<IFoo>();
mock.Setup(foo => foo.Execute("ping"))
    .Callback(() => calls++);

// access invocation arguments
mock.Setup(foo => foo.Execute(It.IsAny<string>()))
    .Callback((string s) => calls.Add(s));

// alternate equivalent generic method syntax
mock.Setup(foo => foo.Execute(It.IsAny<string>()))
    .Callback<string>(s => calls.Add(s));

// access arguments for methods with multiple parameters
mock.Setup(foo => foo.Execute(It.IsAny<int>(), It.IsAny<string>()))
    .Callback<int, string>((i, s) => calls.Add(s));

// callbacks can be specified before and after invocation
mock.Setup(foo => foo.Execute("ping"))
    .Callback(() => Console.WriteLine("Before returns"))
    .Callback(() => Console.WriteLine("After returns"));


mock.Verify(foo => foo.Execute("ping"));

// Verify with custom error message for failure
mock.Verify(foo => foo.Execute("ping"), "When doing operation X, the service should be pinged always");

// Method should never be called
mock.Verify(foo => foo.Execute("ping"), Times.Never());

// Called at least once
mock.Verify(foo => foo.Execute("ping"), Times.AtLeastOnce());

// Verify getter invocation, regardless of value.
mock.VerifyGet(foo => foo.Name);

// Verify setter invocation, regardless of value.
mock.VerifySet(foo => foo.Name);

// Verify setter called with specific value
mock.VerifySet(foo => foo.Name ="foo");

// Verify setter with an argument matcher
mock.VerifySet(foo => foo.Value = It.IsInRange(1, 5, Range.Inclusive));

Customizing Mock Behavior

  • Make mock behave like a "true Mock", raising exceptions for anything that doesn't have a corresponding expectation: in Moq slang a "Strict" mock; default behavior is "Loose" mock, which never throws and returns default values or empty arrays, enumerables, etc. if no expectation is set for a member

    var mock = new Mock<IFoo>(MockBehavior.Strict);
  • Invoke base class implementation if no expectation overrides the member (a.k.a. "Partial Mocks" in Rhino Mocks): default is false. (this is required if you are mocking Web/Html controls in System.Web!)

    var mock = new Mock<IFoo> { CallBase = true };
  • Make an automatic recursive mock: a mock that will return a new mock for every member that doesn't have an expectation and whose return value can be mocked (i.e. it is not a value type)

    var mock = new Mock<IFoo> { DefaultValue = DefaultValue.Mock };
    // default is DefaultValue.Empty
    // this property access would return a new mock of IBar as it's "mock-able"
    IBar value = mock.Object.Bar;
    // the returned mock is reused, so further accesses to the property return 
    // the same mock instance. this allows us to also use this instance to 
    // set further expectations on it if we want
    var barMock = Mock.Get(value);
    barMock.Setup(b => b.Submit()).Returns(true);
  • Centralizing mock instance creation and management: you can create and verify all mocks in a single place by using a MockFactory, which allows setting the MockBehavior, its CallBase and DefaultValue consistently

    var factory = new MockFactory(MockBehavior.Strict) { DefaultValue = DefaultValue.Mock };
    // Create a mock using the factory settings
    var fooMock = factory.Create<IFoo>();
    // Create a mock overriding the factory settings
    var barMock = factory.Create<IBar>(MockBehavior.Loose);
    // Verify all verifiable expectations on all mocks created through the factory


  • Setting expectations for protected members (you can't get intellisense for these, so you access them using the member name as a string):

    // at the top of the test fixture
    using Moq.Protected;
    // in the test
    var mock = new Mock<CommandBase>();
    // if you need argument matching, you MUST use ItExpr rather than It
    // planning on improving this for vNext

Advanced Features

// get mock from a mocked instance
IFoo foo = // get mock instance somehow
var fooMock = Mock.Get(foo);
fooMock.Setup(f => f.Submit()).Returns(true);

// implementing multiple interfaces in mock
var foo = new Mock<IFoo>();
var disposableFoo = foo.As<IDisposable>();
// now the IFoo mock also implements IDisposable :)
disposableFoo.Setup(df => df.Dispose());

//implementing multiple interfaces in single mock
var foo = new Mock<IFoo>();
foo.Setup(f => f.Bar()).Returns("Hello World");
foo.As<IDisposable>().Setup(df => df.Dispose());

// custom matchers
mock.Setup(foo => foo.Submit(IsLarge())).Throws<ArgumentException>();
public string IsLarge() 
  return Match.Create<string>(s => !String.IsNullOrEmpty(s) && s.Length > 100);
  • Mocking internal types of another project: add the following assembly attribute (typically to the AssemblyInfo.cs) to the project containing the internal types:

    // This assembly is the default dynamic assembly generated Castle DynamicProxy, 
    // used by Moq. Paste in a single line.   

Note: when you need to pass the mock for consumption, you must use the mock.Object accessor as a consequence of a C# compiler restriction (vote to get it removed at Microsoft Connect)

Note2: above link is currently dead. Last checked 2016-01-23. Also, what is the restriction? The note above piques curiosity.

Linq to Mocks

Moq is the one and only mocking framework that allows specifying mock behavior via declarative specification queries. You can think of Linq to Mocks as:

from the universe of mocks, get me one/those that behave like this (by Fernando Simonazzi)

Keep that query form in mind when reading the specifications:

var services = Mock.Of<IServiceProvider>(sp =>
    sp.GetService(typeof(IRepository)) == Mock.Of<IRepository>(r => r.IsAuthenticated == true) &&
    sp.GetService(typeof(IAuthentication)) == Mock.Of<IAuthentication>(a => a.AuthenticationType == "OAuth"));

// Multiple setups on a single mock and its recursive mocks
ControllerContext context = Mock.Of<ControllerContext>(ctx =>
     ctx.HttpContext.User.Identity.Name == "kzu" &&
     ctx.HttpContext.Request.IsAuthenticated == true &&
     ctx.HttpContext.Request.Url == new Uri("http://moqthis.com") &&
     ctx.HttpContext.Response.ContentType == "application/xml");

// Setting up multiple chained mocks:
var context = Mock.Of<ControllerContext>(ctx =>
     ctx.HttpContext.Request.Url == new Uri("http://moqthis.me") &&
     ctx.HttpContext.Response.ContentType == "application/xml" &&
     // Chained mock specification
     ctx.HttpContext.GetSection("server") == Mock.Of<ServerSection>(config =>
         config.Server.ServerUrl == new Uri("http://moqthis.com/api"));

Linq to Mocks is great for quickly stubbing out dependencies that typically don't need further verification. If you do need to verify later some invocation on those mocks, you can easily retrieve them with Mock.Get(instance).