Implemented .ShouldReturn().ActionResult() (#359)

Author: ivaylokenov

src/MyTested.AspNetCore.Mvc.Controllers/Builders/Actions/ShouldReturn/ShouldReturnActionResultTestBuilder.cs

@@ -1,8 +1,11 @@
 namespace MyTested.AspNetCore.Mvc.Builders.Actions.ShouldReturn
 {
+    using And;
     using Contracts.Actions;
     using Contracts.And;
     using Internal.TestContexts;
+    using Microsoft.AspNetCore.Mvc;
+    using Utilities.Validators;
 
     /// <summary>
     /// Used for testing returned <see cref="Microsoft.AspNetCore.Mvc.ActionResult"/>.
@@ -23,8 +26,12 @@ public ShouldReturnActionResultTestBuilder(ControllerTestContext testContext)
         /// <inheritdoc />
         public new IAndTestBuilder ActionResult()
         {
-            var result = base.ActionResult;
-            throw new System.NotImplementedException();
+            InvocationResultValidator.ValidateInvocationResultTypes(
+                this.TestContext,
+                canBeAssignable: true,
+                typesOfExpectedReturnValue: new [] { typeof(IActionResult), typeof(ActionResult<>) });
+
+            return new AndTestBuilder(this.TestContext);
         }
     }
 }