Add tests for PowerSum (#3603)

src/test/java/com/thealgorithms/backtracking/PowerSumTest.java

@@ -0,0 +1,28 @@
+package com.thealgorithms.backtracking;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import org.junit.jupiter.api.Test;
+
+public class PowerSumTest {
+
+    @Test
+    void testNumberZeroAndPowerZero() {
+        PowerSum powerSum = new PowerSum();
+        int result = powerSum.powSum(0, 0);
+        assertEquals(1, result);
+    }
+
+    @Test
+    void testNumberHundredAndPowerTwo() {
+        PowerSum powerSum = new PowerSum();
+        int result = powerSum.powSum(100, 2);
+        assertEquals(3, result);
+    }
+  
+    @Test
+    void testNumberHundredAndPowerThree() {
+        PowerSum powerSum = new PowerSum();
+        int result = powerSum.powSum(100, 3);
+        assertEquals(1, result);
+    }
+    
+}