Added checks in CoyoteRuntime.RunTestAsync() to check testMethod if it is either a Action<ICoyoteRuntime> or Func<ICoyoteRuntime, Task> delegate type before calling the runtime extension RunTest() method

[kzdev-net]

The runTest that acts as the top-level execution for the ControlledThread that is created in CoyoteRuntime.RunTestAsync first calls
if (this.Extension.RunTest(testMethod, out Task extensionTask))
before checking if testMethod is an Action or a Func.
When this.Extension is an ActorExecutionContext, then the RunTest method is implemented like so

        bool IRuntimeExtension.RunTest(Delegate test, out Task task)
        {
            if (test is Action<IActorRuntime> actionWithRuntime)
            {
                actionWithRuntime(this);
                task = Task.CompletedTask;
                return true;
            }
            else if (test is Func<IActorRuntime, Task> functionWithRuntime)
            {
                task = functionWithRuntime(this);
                return true;
            }

            task = Task.CompletedTask;
            return false;
        }

However, the Action<T> and Func<T,Task> generic parameter 'T' is contravarient. So, if the testMethod is either an Action<ICoyoteRuntime> or a Func<ICoyoteRuntime, Task>, one of the condition tests will pass, and the method will be executed. Which is fine, but it masks/hides a possible condition where if the runtime extension is not an ActorExecutionContext instance and instead returns false, then the conditional checks in the runTest delegate for the ControlledThread will throw an exception stating that the test delegate type is unsupported even though the TestEngine.Create overloads allow and support such a test method.

        /// <summary>
        /// Creates a new systematic testing engine.
        /// </summary>
        public static TestingEngine Create(Configuration configuration, Action<ICoyoteRuntime> test) =>
            new TestingEngine(configuration, test, new LogWriter(configuration, true));

        /// <summary>
        /// Creates a new systematic testing engine.
        /// </summary>
        public static TestingEngine Create(Configuration configuration, Func<ICoyoteRuntime, Task> test) =>
            new TestingEngine(configuration, test, new LogWriter(configuration, true));

There needs to be type checks in the testMethod prior to calling this.Extension.RunTest().

      if (testMethod is Action<ICoyoteRuntime> actionWithRuntime)
      {
          actionWithRuntime(this);
      }
      else if (testMethod is Func<ICoyoteRuntime, Task> functionWithRuntime)
      {
          task = functionWithRuntime(this);
      }
      else if (this.Extension.RunTest(testMethod, out Task extensionTask))
      {
        ...
      }

[kzdev-net]

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