C#: Add unit test.

Author: michaelnebel

csharp/extractor/Semmle.Extraction.Tests/OverlayInfo.cs

@@ -0,0 +1,30 @@
+using Xunit;
+using Semmle.Util;
+using Semmle.Extraction.CSharp;
+
+namespace Semmle.Extraction.Tests
+{
+    public class OverlayTests
+    {
+        [Fact]
+        public void TestOverlay()
+        {
+            var logger = new LoggerStub();
+            var json =
+                """
+                {
+                    "changes": [
+                        "app/controllers/about_controller.xyz",
+                        "app/models/about.xyz"
+                    ]
+                }
+                """;
+            var overlay = new OverlayInfo(logger, json);
+
+            Assert.True(overlay.IsOverlayMode);
+            Assert.False(overlay.OnlyMakeScaffold("app/controllers/about_controller.xyz"));
+            Assert.False(overlay.OnlyMakeScaffold("app/models/about.xyz"));
+            Assert.True(overlay.OnlyMakeScaffold("app/models/unchanged.xyz"));
+        }
+    }
+}