Add a unit test for merging duplicated yaml nodes.

OpenRA.Test/OpenRA.Game/MiniYamlTest.cs

@@ -169,5 +169,30 @@ TestB:
 			var result = MiniYaml.FromString(yaml).First(n => n.Key == "TestB");
 			Assert.AreEqual(5, result.Location.Line);
 		}
+
+		[TestCase(TestName = "Duplicated nodes are correctly merged")]
+		public void TestSelfMerging()
+		{
+			var baseYaml = @"
+Test:
+	Merge: original
+		Child: original
+	Original:
+Test:
+	Merge: override
+		Child: override
+	Override:
+";
+
+			var result = MiniYaml.Merge(new[] { baseYaml }.Select(s => MiniYaml.FromString(s, "")));
+			Assert.That(result.Count(n => n.Key == "Test"), Is.EqualTo(1), "Result should have exactly one Test node.");
+
+			var testNodes = result.First(n => n.Key == "Test").Value.Nodes;
+			Assert.That(testNodes.Select(n => n.Key), Is.EqualTo(new[] { "Merge", "Original", "Override" }), "Merged Test node has incorrect child nodes.");
+
+			var mergeNode = testNodes.First(n => n.Key == "Merge").Value;
+			Assert.That(mergeNode.Value, Is.EqualTo("override"), "Merge node has incorrect value.");
+			Assert.That(mergeNode.Nodes[0].Value.Value, Is.EqualTo("override"), "Merge node Child value should be 'override', but is not");
+		}
 	}
 }