test(datasync): add Match & Extract mode tests for RegexTransformer

Tests cover:
- Extracting first capture group
- NonMatchBehavior: KeepOriginal, ReturnNull, ReturnEmpty

NEW/tests/JdeScoping.DataSync.Tests/Etl/Transformers/RegexTransformerTests.cs

@@ -29,6 +29,97 @@ public class RegexTransformerTests
         Assert.Equal("Test", reader.GetValue(1)); // Other column unchanged
     }
 
+    [Fact]
+    public void MatchExtract_ExtractsFirstCaptureGroup()
+    {
+        // Arrange
+        var source = CreateMockReader(
+            columns: new[] { "Code" },
+            values: new object[] { "ID_12345" });
+
+        var transformer = new RegexTransformer(
+            columnName: "Code",
+            pattern: @"ID_(\d+)",
+            replacement: null); // null = Match & Extract mode
+
+        // Act
+        var reader = transformer.Transform(source);
+        source.Read().Returns(true);
+        reader.Read();
+
+        // Assert
+        Assert.Equal("12345", reader.GetValue(0));
+    }
+
+    [Fact]
+    public void MatchExtract_NoMatch_KeepOriginal()
+    {
+        // Arrange
+        var source = CreateMockReader(
+            columns: new[] { "Code" },
+            values: new object[] { "UNKNOWN" });
+
+        var transformer = new RegexTransformer(
+            columnName: "Code",
+            pattern: @"ID_(\d+)",
+            replacement: null,
+            nonMatchBehavior: NonMatchBehavior.KeepOriginal);
+
+        // Act
+        var reader = transformer.Transform(source);
+        source.Read().Returns(true);
+        reader.Read();
+
+        // Assert
+        Assert.Equal("UNKNOWN", reader.GetValue(0));
+    }
+
+    [Fact]
+    public void MatchExtract_NoMatch_ReturnNull()
+    {
+        // Arrange
+        var source = CreateMockReader(
+            columns: new[] { "Code" },
+            values: new object[] { "UNKNOWN" });
+
+        var transformer = new RegexTransformer(
+            columnName: "Code",
+            pattern: @"ID_(\d+)",
+            replacement: null,
+            nonMatchBehavior: NonMatchBehavior.ReturnNull);
+
+        // Act
+        var reader = transformer.Transform(source);
+        source.Read().Returns(true);
+        reader.Read();
+
+        // Assert
+        Assert.Equal(DBNull.Value, reader.GetValue(0));
+    }
+
+    [Fact]
+    public void MatchExtract_NoMatch_ReturnEmpty()
+    {
+        // Arrange
+        var source = CreateMockReader(
+            columns: new[] { "Code" },
+            values: new object[] { "UNKNOWN" });
+
+        var transformer = new RegexTransformer(
+            columnName: "Code",
+            pattern: @"ID_(\d+)",
+            replacement: null,
+            nonMatchBehavior: NonMatchBehavior.ReturnEmpty);
+
+        // Act
+        var reader = transformer.Transform(source);
+        source.Read().Returns(true);
+        reader.Read();
+
+        // Assert
+        Assert.Equal(string.Empty, reader.GetValue(0));
+    }
+
     private static IDataReader CreateMockReader(string[] columns, object[] values)
     {
         var reader = Substitute.For<IDataReader>();