Add storage fill test (#15758)

Content.IntegrationTests/PoolManager.cs

@@ -670,6 +670,25 @@ we are just going to end this here to save a lot of time. This is the exception
 
         Assert.That(passed);
     }
+
+    /// <summary>
+    ///     Helper method that retrieves all entity prototypes that have some component.
+    /// </summary>
+    public static List<EntityPrototype> GetEntityPrototypes<T>(RobustIntegrationTest.IntegrationInstance instance) where T : Component
+    {
+        var protoMan = instance.ResolveDependency<IPrototypeManager>();
+        var compFact = instance.ResolveDependency<IComponentFactory>();
+
+        var id = compFact.GetComponentName(typeof(T));
+        var list = new List<EntityPrototype>();
+        foreach (var ent in protoMan.EnumeratePrototypes<EntityPrototype>())
+        {
+            if (ent.Components.ContainsKey(id))
+                list.Add(ent);
+        }
+
+        return list;
+    }
 }
 
 /// <summary>