Add tests, remove main in DiceThrow/DP.java (#5644)

Author: Hardvan

DIRECTORY.md

@@ -788,6 +788,7 @@
             * [ClimbStairsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/ClimbStairsTest.java)
             * [CoinChangeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/CoinChangeTest.java)
             * [CountFriendsPairingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/CountFriendsPairingTest.java)
+            * [DPTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/DPTest.java)
             * [EditDistanceTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/EditDistanceTest.java)
             * [EggDroppingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/EggDroppingTest.java)
             * [KnapsackMemoizationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/KnapsackMemoizationTest.java)

src/main/java/com/thealgorithms/dynamicprogramming/DiceThrow.java

@@ -9,6 +9,7 @@
 
 /* Hence, storing the results of the solved sub-problems saves time.
 And it can be done using Dynamic Programming(DP).
+// Time Complexity: O(m * n * x) where m is number of faces, n is number of dice and x is given sum.
 Following is implementation of Dynamic Programming approach. */
 // Code ---->
 // Java program to find number of ways to get sum 'x' with 'n'
@@ -43,21 +44,4 @@ public static long findWays(int m, int n, int x) {
 
         return table[n][x];
     }
-
-    public static void main(String[] args) {
-        System.out.println(findWays(4, 2, 1));
-        System.out.println(findWays(2, 2, 3));
-        System.out.println(findWays(6, 3, 8));
-        System.out.println(findWays(4, 2, 5));
-        System.out.println(findWays(4, 3, 5));
-    }
 }
-/*
-OUTPUT:
-0
-2
-21
-4
-6
- */
-// Time Complexity: O(m * n * x) where m is number of faces, n is number of dice and x is given sum.

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

@@ -0,0 +1,56 @@
+package com.thealgorithms.dynamicprogramming;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class DPTest {
+
+    @Test
+    void testSumLessThanMinimumFaceValue() {
+        // When the sum is less than the minimum possible face value
+        // There are 0 ways to achieve the sum
+        assertEquals(0, DP.findWays(4, 2, 1)); // 4 faces, 2 dice, sum = 1
+    }
+
+    @Test
+    void testTwoDiceWithSumEqualToTwo() {
+        // When there are 2 dice and the sum is equal to the number of dice
+        // The only way is to have both dice showing 1
+        assertEquals(1, DP.findWays(2, 2, 2)); // 2 faces, 2 dice, sum = 2
+    }
+
+    @Test
+    void testTwoDiceWithSumThree() {
+        // When there are 2 dice and the sum is equal to 3
+        // Possible combinations are (1,2) and (2,1)
+        assertEquals(2, DP.findWays(2, 2, 3)); // 2 faces, 2 dice, sum = 3
+    }
+
+    @Test
+    void testThreeDiceWithSumEight() {
+        // Test for 3 dice, each having 6 faces
+        // Possible combinations to make sum of 8
+        assertEquals(21, DP.findWays(6, 3, 8)); // 6 faces, 3 dice, sum = 8
+    }
+
+    @Test
+    void testTwoDiceWithSumFive() {
+        // Test for 2 dice, with 4 faces to make sum of 5
+        // Possible combinations: (1,4), (2,3), (3,2), (4,1)
+        assertEquals(4, DP.findWays(4, 2, 5)); // 4 faces, 2 dice, sum = 5
+    }
+
+    @Test
+    void testThreeDiceWithSumFive() {
+        // Test for 3 dice, with 4 faces to make sum of 5
+        // Possible combinations: (1,1,3), (1,2,2), (1,3,1), (2,1,2), (2,2,1), (3,1,1)
+        assertEquals(6, DP.findWays(4, 3, 5)); // 4 faces, 3 dice, sum = 5
+    }
+
+    @Test
+    void testEdgeCaseZeroSum() {
+        // Test for 0 sum with 0 dice
+        assertEquals(0, DP.findWays(4, 0, 0)); // 4 faces, 0 dice, sum = 0
+    }
+}