diff --git a/RecursiveDigitSumTest.java b/RecursiveDigitSumTest.java
new file mode 100644
index 00000000..903edbfe
--- /dev/null
+++ b/RecursiveDigitSumTest.java
@@ -0,0 +1,127 @@
+package recursion;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import javax.annotation.processing.Generated;
+
+import org.junit.AfterClass;
+import org.junit.Assert;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+@Generated(value = "org.junit-tools-1.1.0")
+public class RecursiveDigitSumTest {
+
+	@BeforeClass
+	public static void setUpBeforeClass() throws Exception {
+		System.out.println("BeforeClass");
+	}
+
+	@AfterClass
+	public static void tearDownAfterClass() throws Exception {
+		System.out.println("AfterClass");
+	}
+
+	@Test
+	public void testSuperDigitWithNull() throws Exception {
+		// TC1
+		int k = 0;
+		String n = null;
+		String expected = "by input exception [" + n + "]";
+		Exception result = assertThrows(Exception.class, 
+				() -> RecursiveDigitSum.superDigit(n, k));
+		
+		Assert.assertEquals(expected, result.getMessage());
+	}
+
+	@Test
+	public void testSuperDigitWithEmpty() throws Exception {
+		// TC2
+		int k = 1;
+		String n = "";
+		int expected = 0;
+		int result = RecursiveDigitSum.superDigit(n, k);
+		
+		Assert.assertEquals(expected, result);
+	}
+
+	@Test
+	public void testSuperDigitWithNegative1() throws Exception {
+		// TC3
+		int k = -1;
+		String n = "1";
+		String expected = "by input exception [" + k + "]";
+		Exception result = assertThrows(Exception.class, 
+				() -> RecursiveDigitSum.superDigit(n, k));
+		
+		Assert.assertEquals(expected, result.getMessage());
+	}
+
+	@Test
+	public void testSuperDigit1() throws Exception {
+		// TC4
+		int k = 0;
+		String n = "1";
+		int expected = 1;
+		int result = RecursiveDigitSum.superDigit(n, k);
+		
+		Assert.assertEquals(expected, result);
+	}
+
+	@Test
+	public void testSuperDigitMax1() throws Exception {
+		// TC5
+		int k = 999999999;
+		String n = "1";
+		int expected = 9;
+		int result = RecursiveDigitSum.superDigit(n, k);
+		
+		Assert.assertEquals(expected, result);
+	}
+
+	@Test
+	public void testSuperDigit3() throws Exception {
+		// TC6
+		int k = 0;
+		String n = "12";
+		int expected = 3;
+		int result = RecursiveDigitSum.superDigit(n, k);
+		
+		Assert.assertEquals(expected, result);
+	}
+
+	@Test
+	public void testSuperDigit4() throws Exception {
+		// TC7
+		int k = 1;
+		String n = "12";
+		int expected = 3;
+		int result = RecursiveDigitSum.superDigit(n, k);
+		
+		Assert.assertEquals(expected, result);
+	}
+
+	@Test
+	public void testSuperDigitMax2() throws Exception {
+		// TC8
+		int k = 1;
+		String n = "999999999";
+		int expected = 9;
+		int result = RecursiveDigitSum.superDigit(n, k);
+		
+		Assert.assertEquals(expected, result);
+	}
+
+	@Test
+	public void testSuperDigitWithNegative2() throws Exception {
+		// TC9
+		int k = 1;
+		String n = "-a";
+		String expected = "by input exception [" + n + "]";
+		Exception result = assertThrows(Exception.class, 
+				() -> RecursiveDigitSum.superDigit(n, k));
+		
+		Assert.assertEquals(expected, result.getMessage());
+	}
+
+}
\ No newline at end of file
diff --git a/RecursiveDigitSumTest2.java b/RecursiveDigitSumTest2.java
new file mode 100644
index 00000000..c1085ad2
--- /dev/null
+++ b/RecursiveDigitSumTest2.java
@@ -0,0 +1,127 @@
+package recursion;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import javax.annotation.processing.Generated;
+
+import org.junit.AfterClass;
+import org.junit.Assert;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+@Generated(value = "org.junit-tools-1.1.0")
+public class RecursiveDigitSumTest2 {
+
+	@BeforeClass
+	public static void setUpBeforeClass() throws Exception {
+		System.out.println("BeforeClass");
+	}
+
+	@AfterClass
+	public static void tearDownAfterClass() throws Exception {
+		System.out.println("AfterClass");
+	}
+
+	@Test
+	public void testSuperDigitWithNull() throws Exception {
+		// TC1
+		int k = 0;
+		String n = null;
+		String expected = "by input exception [" + n + "]";
+		Exception result = assertThrows(Exception.class, 
+				() -> RecursiveDigitSum2.superDigit(n, k));
+		
+		Assert.assertEquals(expected, result.getMessage());
+	}
+
+	@Test
+	public void testSuperDigitWithEmpty() throws Exception {
+		// TC2
+		int k = 1;
+		String n = "";
+		int expected = 0;
+		int result = RecursiveDigitSum2.superDigit(n, k);
+		
+		Assert.assertEquals(expected, result);
+	}
+
+	@Test
+	public void testSuperDigitWithNegative1() throws Exception {
+		// TC3
+		int k = -1;
+		String n = "1";
+		String expected = "by input exception [" + k + "]";
+		Exception result = assertThrows(Exception.class, 
+				() -> RecursiveDigitSum2.superDigit(n, k));
+		
+		Assert.assertEquals(expected, result.getMessage());
+	}
+
+	@Test
+	public void testSuperDigit1() throws Exception {
+		// TC4
+		int k = 0;
+		String n = "1";
+		int expected = 1;
+		int result = RecursiveDigitSum2.superDigit(n, k);
+		
+		Assert.assertEquals(expected, result);
+	}
+
+	@Test
+	public void testSuperDigitMax1() throws Exception {
+		// TC5
+		int k = 999999999;
+		String n = "1";
+		int expected = 9;
+		int result = RecursiveDigitSum2.superDigit(n, k);
+		
+		Assert.assertEquals(expected, result);
+	}
+
+	@Test
+	public void testSuperDigit3() throws Exception {
+		// TC6
+		int k = 0;
+		String n = "12";
+		int expected = 3;
+		int result = RecursiveDigitSum2.superDigit(n, k);
+		
+		Assert.assertEquals(expected, result);
+	}
+
+	@Test
+	public void testSuperDigit4() throws Exception {
+		// TC7
+		int k = 1;
+		String n = "12";
+		int expected = 3;
+		int result = RecursiveDigitSum2.superDigit(n, k);
+		
+		Assert.assertEquals(expected, result);
+	}
+
+	@Test
+	public void testSuperDigitMax2() throws Exception {
+		// TC8
+		int k = 1;
+		String n = "999999999";
+		int expected = 9;
+		int result = RecursiveDigitSum2.superDigit(n, k);
+		
+		Assert.assertEquals(expected, result);
+	}
+
+	@Test
+	public void testSuperDigitWithNegative2() throws Exception {
+		// TC9
+		int k = 1;
+		String n = "-a";
+		String expected = "by input exception [" + n + "]";
+		Exception result = assertThrows(Exception.class, 
+				() -> RecursiveDigitSum2.superDigit(n, k));
+		
+		Assert.assertEquals(expected, result.getMessage());
+	}
+
+}
\ No newline at end of file