Add tests for Selection Sort (#3091)

src/test/java/com/thealgorithms/maths/SumOfDigitsTest.java

@@ -1,25 +1,31 @@
-package com.thealgorithms.maths;
-
-import org.junit.jupiter.api.Test;
-
-import static org.junit.jupiter.api.Assertions.assertEquals;
-
-/**
- * @author SirFixalot16
- * @since 01/06/22
- */
-public class SumOfDigitsTest {
-    @Test
-    void isSumOf2Digits() {
-        SumOfDigits sum = new SumOfDigits();
-        assertEquals(11, sum.sumOfDigits(56));
-    }
-    void isSumOf3Digits() {
-        SumOfDigits sum = new SumOfDigits();
-        assertEquals(12, sum.sumOfDigits(192));
-    }
-    void isSumOf4Digits() {
-        SumOfDigits sum = new SumOfDigits();
-        assertEquals(25, sum.sumOfDigits(8962));
-    }
-}
+package com.thealgorithms.maths;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class SumOfDigitsTest {
+
+    SumOfDigits SoD = new SumOfDigits();
+
+    @Test
+    void testZero() {
+        assertEquals(0, SoD.sumOfDigits(0));
+        assertEquals(0, SoD.sumOfDigitsRecursion(0));
+        assertEquals(0, SoD.sumOfDigitsFast(0));
+    }
+
+    @Test
+    void testPositive() {
+        assertEquals(15, SoD.sumOfDigits(12345));
+        assertEquals(15, SoD.sumOfDigitsRecursion(12345));
+        assertEquals(15, SoD.sumOfDigitsFast(12345));
+    }
+
+    @Test
+    void testNegative() {
+        assertEquals(6, SoD.sumOfDigits(-123));
+        assertEquals(6, SoD.sumOfDigitsRecursion(-123));
+        assertEquals(6, SoD.sumOfDigitsFast(-123));
+    }
+}