Improve integration testing

Content.IntegrationTests/DummyParallaxManager.cs

@@ -0,0 +1,25 @@
+using System;
+using Content.Client.Interfaces.Parallax;
+using Robust.Client.Graphics;
+
+namespace Content.IntegrationTests
+{
+    public sealed class DummyParallaxManager : IParallaxManager
+    {
+        public event Action<Texture> OnTextureLoaded
+        {
+            add
+            {
+            }
+            remove
+            {
+            }
+        }
+
+        public Texture ParallaxTexture => null;
+
+        public void LoadParallax()
+        {
+        }
+    }
+}