add Test_StructuralChange_Docs

src/Tests/ECS/Arch/Test_StructuralChange_Docs.cs

@@ -0,0 +1,25 @@
+using System.Collections.Generic;
+using NUnit.Framework;
+
+
+// ReSharper disable ConditionalTernaryEqualBranch
+// ReSharper disable CompareOfFloatsByEqualityOperator
+// ReSharper disable StringLiteralTypo
+// ReSharper disable InconsistentNaming
+namespace Tests.ECS.Arch {
+
+public static class Test_StructuralChange_Docs
+{
+[Test]
+public static void CollectionModifiedException()
+{
+    var list = new List<int> { 1, 2, 3 };
+    foreach (var item in list) {
+        list.Add(42); // throws InvalidOperationException : Collection was modified; enumeration operation may not execute.
+    }
+}
+
+}
+
+}
+