State Relation pattern

Question

Hi,

I am a bit confused about the "State Relation" pattern.
In "Parameterized Test Patterns For Effective Testing with Pex" , The applicability of State Relation pattern says""This pattern applies when an API call causes an internal state change that can be (partially) observed through other API calls."

I have the following PexMethod:

      [PexMethod]
      public void CanRegisterTwoObjectsAndGetThemBoth([PexAssumeUnderTest]A o,[PexAssumeUnderTest] object[] objects, [PexAssumeUnderTest] string[] keys)
         {
            ArrayList keylist = new ArrayList();
             ArrayList objectlist = new ArrayList();
            for (int i = 0; i < keys.Length; i++)
               {
                 if (!o.ContainsKey(keys[i]))
                {
                    o.Add(keys[i], objects[i]);
                    keylist.Add(keys[i]);
            objectlist.Add(objects[i]);
               }
        }
             foreach (string key in keylist)
                  {               
           PexAssert.AreSame(o[key], objectlist[keylist.IndexOf(key)]);
        }  
      }
   
I feel that this would fall under State Relation pattern because the "Add" operation on "o" is asserted by checking if "o" now has the object that was added at the index "key". But we do not use any API call here to observe this. Can you please tell me if this would still fall under state relation pattern or will it be some other pattern?

Thanks!

Answer 1

You do use API calls to observe the resulted state change: In your assert, you have "objectlist[...]". This syntax is just syntactic sugar for calling the indexer getter method, defined by "TValue this[TKey index] { get { ... } }" in the code of the class "A".

We might not explicitly mention this in the patterns document, but (implicit) calls to property and indexer getters and setters are also API calls.

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Nikolai Tillmann - Tell us how you use Pex

Answer 2

Thank you very much for clearing my confusion, Nikolai!