Add tests, enhance docs in KadaneAlgorithm.java (#5646)

src/test/java/com/thealgorithms/dynamicprogramming/KadaneAlgorithmTest.java

@@ -0,0 +1,61 @@
+package com.thealgorithms.dynamicprogramming;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+public class KadaneAlgorithmTest {
+
+    @Test
+    void testMaxSumWithPositiveValues() {
+        // Test with all positive numbers
+        int[] input = {89, 56, 98, 123, 26, 75, 12, 40, 39, 68, 91};
+        int expectedMaxSum = 89 + 56 + 98 + 123 + 26 + 75 + 12 + 40 + 39 + 68 + 91; // sum of all elements
+        assertTrue(KadaneAlgorithm.maxSum(input, expectedMaxSum));
+    }
+
+    @Test
+    void testMaxSumWithMixedValues() {
+        // Test with mixed positive and negative numbers
+        int[] input = {1, -2, 3, 4, -1, 2, 1, -5, 4};
+        int expectedMaxSum = 3 + 4 + -1 + 2 + 1; // max subarray is [3, 4, -1, 2, 1]
+        assertTrue(KadaneAlgorithm.maxSum(input, expectedMaxSum));
+    }
+
+    @Test
+    void testMaxSumWithAllNegativeValues() {
+        // Test with all negative numbers
+        int[] input = {-2, -3, -1, -4};
+        int expectedMaxSum = -1; // max subarray is the least negative number
+        assertTrue(KadaneAlgorithm.maxSum(input, expectedMaxSum));
+    }
+
+    @Test
+    void testMaxSumWithSingleElement() {
+        // Test with a single positive element
+        int[] input = {10};
+        int expectedMaxSum = 10; // max subarray is the single element
+        assertTrue(KadaneAlgorithm.maxSum(input, expectedMaxSum));
+
+        // Test with a single negative element
+        input = new int[] {-10};
+        expectedMaxSum = -10; // max subarray is the single element
+        assertTrue(KadaneAlgorithm.maxSum(input, expectedMaxSum));
+    }
+
+    @Test
+    void testMaxSumWithZero() {
+        // Test with zeros in the array
+        int[] input = {0, -1, 2, -2, 0, 3};
+        int expectedMaxSum = 3; // max subarray is [2, -2, 0, 3]
+        assertTrue(KadaneAlgorithm.maxSum(input, expectedMaxSum));
+    }
+
+    @Test
+    void testMaxSumWithEmptyArray() {
+        // Test with an empty array; should ideally throw an exception or return false
+        int[] input = {};
+        assertThrows(ArrayIndexOutOfBoundsException.class, () -> { KadaneAlgorithm.maxSum(input, 0); });
+    }
+}