[Silverlight getting started series] how to unit test unittesting In the event eventaggregator of prism

The previous article explains how to perform unit tests on prism and MEF. Today, let's talk about how to test event publishing and subscription eventaggregator in prism? We all know that eventaggregator is available in Prism:

UsingMicrosoft. Practices. Prism. events;

PrivateIeventaggregator theeventaggregator {Get;Set;}

[Importingconstructor]
PublicMyviewmodel (ieventaggregator eventaggregator)
{
Theeventaggregator=Eventaggregator;
//Todo:
}
 

You can then publish and subscribe the event ):

Theeventaggregator. getevent<Marketpricesupdatedevent>(). Publish (clonedpricelist );
 

AboveCodeA Custom Event: marketpriceupdatedevent: (defined as the data type you need. Here is idictionary <string, decimal>)

Public ClassMarketpricesupdatedevent: compositepresentationevent<Idictionary<String,Decimal>
{
}
 

If the last line of a function is to publish an event without returning a value, how can we perform unit testing on it? How can I test whether this event has been publish?

We can write a mock eventaggregator:

 Class  Mockeventaggregator: ieventaggregator
{
Dictionary  < Type,  Object  >  Events  =     New  Dictionary  <  Type,  Object  >  ();
  Public  Teventtype getevent  <  Teventtype >  ()  Where  Teventtype: eventbase,  New  ()
{
  Return  (Teventtype) events [  Typeof  (Teventtype)];
}

  Public     Void  Addmapping  <  Teventtype >  (Teventtype mockevent)
{
Events. Add (  Typeof  (Teventtype), mockevent );
}
}

  Class  Mockpriceupdatedeventaggregator: mockeventaggregator
{
  Public  Mockmarketpricesupdatedevent mockmarketpriceupdatedevent  =     New  Mockmarketpricesupdatedevent ();
  Public Mockpriceupdatedeventaggregator ()
{
  //  Note that this is not mock, it is the original one!  
  Addmapping  <  Marketpricesupdatedevent  >  (Mockmarketpriceupdatedevent );
}

  Public     Class  Mockmarketpricesupdatedevent: marketpricesupdatedevent
{
  Public    Bool  Publishcalled;
  Public  Idictionary  <  String  ,  Decimal  >  Publishargumentpayload;
  Public  Eventhandler publishcalledevent;

  Private     Void Onpublishcalledevent (  Object  Sender, eventargs ARGs)
{
  If  (Publishcalledevent  ! =     Null  )
Publishcalledevent (sender, argS );
}

  Public     Override     Void  Publish (idictionary <  String  ,  Decimal  >  Payload)
{
Publishcalled  =     True  ;
Publishargumentpayload  =  Payload;
Onpublishcalledevent (  This  , Eventargs. Empty );
}
}
} 

Then the mock event can be used in the unit test class:

[Testmethod]
  Public     Void  Testpublishedevent ()
{
VaR eventagregator  =     New  Mockpriceupdatedeventaggregator ();
VaR marketfeed  =     New  Testablemarketfeedservice (eventagregator );
Assert. istrue (marketfeed. symbolexists (  " Stock0  "  ));

Marketfeed. invokeupdateprices ();

  //  Verify event Publishing  
  Assert. istrue (eventagregator. mockmarketpriceupdatedevent. publishcalled );

  //  Validate event parameters  
  VaR Payload  =  Eventagregator. mockmarketpriceupdatedevent. publishargumentpayload;
Assert. isnotnull (payload );
Assert. istrue (payload. containskey ( "  Stock0  "  ));
Assert. areequal (marketfeed. getprice (  "  Stock0  "  ), Payload [  "  Stock0  "  ]);
}