Assigning out ref parameters in Moq

Question

Is it possible to assign an out ref parameter using Moq  3 0     I ve looked at using Callback    but Action lt  gt  does not support ref parameters because it s based on generics  I d also preferably like to put a constraint  It Is  on the input of the ref parameter  though I can do that in the callback   I know that Rhino Mocks supports this functionality  but the project I m working on is already using Moq

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Moq version 4 8  or later  has much improved support for by-ref parameters   public interface IGobbler       bool Gobble ref int amount      delegate void GobbleCallback ref int amount          needed for Callback delegate bool GobbleReturns ref int amount           needed for Returns  var mock   new Mock lt IGobbler gt     mock Setup m   gt  m Gobble ref It Ref lt int gt  IsAny       match any value passed by-ref      Callback new GobbleCallback  ref int amount    gt                  if  amount  gt  0                          Console WriteLine  Gobbling                    amount -  1                           Returns new GobbleReturns  ref int amount    gt  amount  gt  0     int a   5  bool gobbleSomeMore   true  while  gobbleSomeMore        gobbleSomeMore   mock Object Gobble ref a       The same pattern works for out parameters   It Ref lt T gt  IsAny also works for C  7 in parameters  since they are also by-ref

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Building on Billy Jakes awnser  I made a fully dynamic mock method with an out parameter  I m posting this here for anyone who finds it usefull     Define a delegate with the params of the method that returns void  delegate void methodDelegate int x  out string output       Define a variable to store the return value  bool returnValue      Mock the method      Do all logic in  Callback and store the return value     Then return the return value in the  Returns mockHighlighter Setup h   gt  h SomeMethod It IsAny lt int gt     out It Ref lt int gt  IsAny      Callback new methodDelegate  int x  out int output    gt             do some logic to set the output and return value      output           returnValue                Returns      gt  returnValue

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To return a value along with setting ref parameter  here is a piece of code   public static class MoqExtensions       public static IReturnsResult lt TMock gt  DelegateReturns lt TMock  TReturn  T gt  this IReturnsThrows lt TMock  TReturn gt  mock  T func  where T   class         where TMock   class               mock GetType   Assembly GetType  Moq MethodCallReturn 2   MakeGenericType typeof TMock   typeof TReturn                InvokeMember  SetReturnDelegate   BindingFlags InvokeMethod   BindingFlags NonPublic   BindingFlags Instance  null  mock                  new     func             return  IReturnsResult lt TMock gt  mock            Then declare your own delegate matching the signature of to-be-mocked method and provide your own method implementation   public delegate int MyMethodDelegate int x  ref int y         TestMethod      public void TestSomething                   Arrange         var mock   new Mock lt ISomeInterface gt             var y   0          mock Setup m   gt  m MyMethod It IsAny lt int gt     ref y            DelegateReturns  MyMethodDelegate   int x  ref int y   gt                         y   1              return 2

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EDIT  In Moq 4 10  you can now pass a delegate that has an out or ref parameter directly to the Callback function    mock    Setup x  gt x Method out d      Callback myDelegate     Returns          You will have to define a delegate and instantiate it         Callback new MyDelegate  out decimal v   gt v 12m         For Moq version before 4 10   Avner Kashtan provides an extension method in his blog which allows setting the out parameter from a callback  Moq  Callbacks and Out parameters  a particularly tricky edge case  The solution is both elegant and hacky  Elegant in that it provides a fluent syntax that feels at-home with other Moq callbacks  And hacky because it relies on calling some internal Moq APIs via reflection   The extension method provided at the above link didn t compile for me  so I ve provided an edited version below  You ll need to create a signature for each number of input parameters you have  I ve provided 0 and 1  but extending it further should be simple   public static class MoqExtensions       public delegate void OutAction lt TOut gt  out TOut outVal       public delegate void OutAction lt in T1 TOut gt  T1 arg1  out TOut outVal        public static IReturnsThrows lt TMock  TReturn gt  OutCallback lt TMock  TReturn  TOut gt  this ICallback lt TMock  TReturn gt  mock  OutAction lt TOut gt  action          where TMock   class               return OutCallbackInternal mock  action              public static IReturnsThrows lt TMock  TReturn gt  OutCallback lt TMock  TReturn  T1  TOut gt  this ICallback lt TMock  TReturn gt  mock  OutAction lt T1  TOut gt  action          where TMock   class               return OutCallbackInternal mock  action              private static IReturnsThrows lt TMock  TReturn gt  OutCallbackInternal lt TMock  TReturn gt  ICallback lt TMock  TReturn gt  mock  object action          where TMock   class               mock GetType                Assembly GetType  Moq MethodCall                InvokeMember  SetCallbackWithArguments   BindingFlags InvokeMethod   BindingFlags NonPublic   BindingFlags Instance  null  mock                  new     action             return mock as IReturnsThrows lt TMock  TReturn gt             With the above extension method  you can test an interface with out parameters such as   public interface IParser       bool TryParse string token  out int value          with the following Moq setup        TestMethod      public void ParserTest                 Mock lt IParser gt  parserMock   new Mock lt IParser gt              int outVal          parserMock              Setup p   gt  p TryParse  6   out outVal                OutCallback  string t  out int v    gt  v   6               Returns true            int actualValue          bool ret   parserMock Object TryParse  6   out actualValue            Assert IsTrue ret           Assert AreEqual 6  actualValue            Edit  To support void-return methods  you simply need to add new overload methods   public static ICallbackResult OutCallback lt TOut gt  this ICallback mock  OutAction lt TOut gt  action        return OutCallbackInternal mock  action      public static ICallbackResult OutCallback lt T1  TOut gt  this ICallback mock  OutAction lt T1  TOut gt  action        return OutCallbackInternal mock  action      private static ICallbackResult OutCallbackInternal ICallback mock  object action        mock GetType   Assembly GetType  Moq MethodCall            InvokeMember  SetCallbackWithArguments   BindingFlags InvokeMethod   BindingFlags NonPublic   BindingFlags Instance  null  mock  new     action         return  ICallbackResult mock      This allows testing interfaces such as   public interface IValidationRule       void Validate string input  out string message       TestMethod  public void ValidatorTest         Mock lt IValidationRule gt  validatorMock   new Mock lt IValidationRule gt          string outMessage      validatorMock          Setup v   gt  v Validate  input   out outMessage            OutCallback  string i  out string m    gt  m     success         string actualMessage      validatorMock Object Validate  input   out actualMessage        Assert AreEqual  success   actualMessage

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I m sure Scott s solution worked at one point    But it s a good argument for not using reflection to peek at private apis  It s broken now   I was able to set out parameters using a delegate         delegate void MockOutDelegate string s  out int value        public void SomeMethod                                int value           myMock Setup x   gt  x TryDoSomething It IsAny lt string gt     out value                Callback new MockOutDelegate  string s  out int output    gt  output   userId                Returns true

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I struggled with many of the suggestions here before I simple created an instance of a new  Fake  class that implements whatever interface you are trying to Mock out  Then you can simply set the value of the out parameter with the method itself

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For  out   the following seems to work for me   public interface IService       void DoSomething out string a       TestMethod  public void Test         var service   new Mock lt IService gt         var expectedValue    value       service Setup s   gt  s DoSomething out expectedValue         string actualValue      service Object DoSomething out actualValue       Assert AreEqual expectedValue  actualValue       I m guessing that Moq looks at the value of  expectedValue  when you call Setup and remembers it   For ref  I m looking for an answer also   I found the following QuickStart guide useful  https   github com Moq moq4 wiki Quickstart

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This is documentation from Moq site      out arguments var outString    ack      TryParse will return true  and the out argument will return  ack   lazy evaluated mock Setup foo   gt  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   gt  foo Submit ref instance   Returns true

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Seems like it is not possible out of the box  Looks like someone attempted a solution   See this forum post http   code google com p moq issues detail id 176  this question  Verify value of reference parameter with Moq

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I struggled with this for an hour this afternoon and could not find an answer anywhere  After playing around on my own with it I was able to come up with a solution which worked for me    string firstOutParam    first out parameter string   string secondOutParam   100  mock SetupAllProperties    mock Setup m  gt m Method out firstOutParam  out secondOutParam   Returns value     The key here is mock SetupAllProperties    which will stub out all of the properties for you  This may not work in every test case scenario  but if all you care about is getting the return value of YourMethod then this will work fine

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This can be a solution     Test  public void TestForOutParameterInMoq         Arrange    mockParameterManager  new Mock lt IParameterManager gt        Mock lt IParameter  gt  mockParameter  new Mock lt IParameter  gt         Parameter affectation should be useless but is not  It s really used by Moq    IParameter parameter  mockParameter Object       Mock method used in UpperParameterManager    mockParameterManager Setup x   gt  x OutMethod out parameter         Act with the real instance    UpperParameterManager UpperOutMethod out parameter        Assert that method used on the out parameter of inner out method are really called   mockParameter Verify x   gt  x FunctionCalledInOutMethodAfterInnerOutMethod   Times Once

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