Add storage fill test (#3352)

Validates amounts (useful) and prototypes (less useful given SpawnEntityTest exists)

Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>

Content.IntegrationTests/Tests/StorageFillTest.cs

@@ -0,0 +1,42 @@
+#nullable enable
+using System.Threading.Tasks;
+using NUnit.Framework;
+using Robust.Shared.Prototypes;
+using Robust.Shared.Utility;
+using YamlDotNet.RepresentationModel;
+
+namespace Content.IntegrationTests.Tests
+{
+    [TestFixture]
+    public sealed class StorageFillTest : ContentIntegrationTest
+    {
+        [Test]
+        public async Task TestStorageFillPrototypes()
+        {
+            var server = StartServerDummyTicker();
+            await server.WaitIdleAsync();
+            var protoManager = server.ResolveDependency<IPrototypeManager>();
+
+            await server.WaitAssertion(() =>
+            {
+                foreach (var proto in protoManager.EnumeratePrototypes<EntityPrototype>())
+                {
+                    if (!proto.Components.TryGetValue("StorageFill", out var storageNode) ||
+                        !storageNode.TryGetNode("contents", out YamlSequenceNode? contentsNode)) continue;
+
+                    foreach (var child in contentsNode)
+                    {
+                        if (child is not YamlMappingNode mapping) continue;
+                        var name = mapping.GetNode("name").AsString();
+                        Assert.That(protoManager.HasIndex<EntityPrototype>(name), $"Unable to find StorageFill prototype of {name} in prototype {proto.ID}");
+
+                        if (mapping.TryGetNode("amount", out var amount))
+                        {
+                            Assert.That(amount.AsInt() > 0, $"Specified invalid amount of {amount} for prototype {proto.ID}");
+                        }
+                    }
+                }
+            });
+        }
+    }
+}