Add material arbitrage tests (#13315)

Content.Server/Construction/Components/MachinePartComponent.cs

@@ -12,5 +12,12 @@ namespace Content.Server.Construction.Components
         [ViewVariables(VVAccess.ReadWrite)]
         [DataField("rating")]
         public int Rating { get; private set; } = 1;
+
+        /// <summary>
+        ///     This number is used in tests to ensure that you can't use high quality machines for arbitrage. In
+        ///     principle there is nothing wrong with using higher quality parts, but you have to be careful to not
+        ///     allow them to be put into a lathe or something like that.
+        /// </summary>
+        public const int MaxRating = 4;
     }
 }