Add unit test asserting that saving, loading & saving the map produces identical output. (#348)

Also fixed PowerProvider violating this.

Content.Server/GameObjects/Components/Power/PowerDevice.cs

@@ -32,6 +32,8 @@ namespace Content.Server.GameObjects.Components.Power
             }
         }
 
+        protected virtual bool SaveLoad => true;
+
         /// <summary>
         ///     The method of draw we will try to use to place our load set via component parameter, defaults to using power providers
         /// </summary>
@@ -191,8 +193,12 @@ namespace Content.Server.GameObjects.Components.Power
             base.ExposeData(serializer);
 
             serializer.DataField(ref _drawType, "drawtype", DrawTypes.Provider);
-            serializer.DataField(ref _load, "load", 100);
             serializer.DataField(ref _priority, "priority", Powernet.Priority.Medium);
+
+            if (SaveLoad)
+            {
+                serializer.DataField(ref _load, "load", 100);
+            }
         }
 
         void IExamine.Examine(FormattedMessage message)

Content.Server/GameObjects/Components/Power/PowerProviderComponent.cs

@@ -23,6 +23,8 @@ namespace Content.Server.GameObjects.Components.Power
         /// <inheritdoc />
         public override DrawTypes DrawType { get; protected set; } = DrawTypes.Node;
 
+        protected override bool SaveLoad => false;
+
         /// <summary>
         /// Variable that determines the range that the power provider will try to supply power to
         /// </summary>
@@ -280,7 +282,7 @@ namespace Content.Server.GameObjects.Components.Power
             // Stops an APC from trying to connect to itself
             if (this == device)
                 return false;
-            
+
             return (device.Owner.Transform.WorldPosition - Owner.Transform.WorldPosition).LengthSquared <= _range;
         }
     }