Update Combinations.java and add test case (#3184)

src/main/java/com/thealgorithms/maths/Combinations.java

@@ -5,23 +5,6 @@ package com.thealgorithms.maths;
  */
 public class Combinations {
 
-    public static void main(String[] args) {
-        assert combinations(1, 1) == 1;
-        assert combinations(10, 5) == 252;
-        assert combinations(6, 3) == 20;
-        assert combinations(20, 5) == 15504;
-
-        // Since, 200 is a big number its factorial will go beyond limits of long even when 200C5 can be saved in a long
-        // variable. So below will fail
-        // assert combinations(200, 5) == 2535650040l;
-        assert combinationsOptimized(100, 0) == 1;
-        assert combinationsOptimized(1, 1) == 1;
-        assert combinationsOptimized(10, 5) == 252;
-        assert combinationsOptimized(6, 3) == 20;
-        assert combinationsOptimized(20, 5) == 15504;
-        assert combinationsOptimized(200, 5) == 2535650040l;
-    }
-
     /**
      * Calculate of factorial
      *

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

@@ -0,0 +1,30 @@
+package com.thealgorithms.maths;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class CombinationsTest {
+
+    @Test
+    void testCombination() {
+
+        assertEquals(1, Combinations.combinations(1, 1));
+        assertEquals(252, Combinations.combinations(10, 5));
+        assertEquals(20, Combinations.combinations(6, 3));
+        assertEquals(15504, Combinations.combinations(20, 5));
+
+    }
+
+    @Test
+    void testCombinationOptimised() {
+
+        assertEquals(100, Combinations.combinationsOptimized(100, 1));
+        assertEquals(1, Combinations.combinationsOptimized(1, 1));
+        assertEquals(252, Combinations.combinationsOptimized(10, 5));
+        assertEquals(20, Combinations.combinationsOptimized(6, 3));
+        assertEquals(15504, Combinations.combinationsOptimized(20, 5));
+        assertEquals(2535650040L, Combinations.combinationsOptimized(200, 5));
+
+    }
+}