Add tests for ClosestPair.java (#5555)

DIRECTORY.md

@@ -741,6 +741,7 @@
               * [ZigzagTraversalTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/ZigzagTraversalTest.java)
           * divideandconquer
             * [BinaryExponentiationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/divideandconquer/BinaryExponentiationTest.java)
+            * [ClosestPairTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/divideandconquer/ClosestPairTest.java)
             * [SkylineAlgorithmTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/divideandconquer/SkylineAlgorithmTest.java)
             * [StrassenMatrixMultiplicationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/divideandconquer/StrassenMatrixMultiplicationTest.java)
           * dynamicprogramming

src/main/java/com/thealgorithms/divideandconquer/ClosestPair.java

@@ -13,7 +13,7 @@ public final class ClosestPair {
     /**
      * Input data, maximum 10000.
      */
-    private Location[] array;
+    Location[] array;
     /**
      * Minimum point coordinate.
      */

src/test/java/com/thealgorithms/divideandconquer/ClosestPairTest.java

@@ -0,0 +1,75 @@
+package com.thealgorithms.divideandconquer;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+import org.junit.jupiter.api.Test;
+
+public class ClosestPairTest {
+
+    @Test
+    public void testBuildLocation() {
+        ClosestPair cp = new ClosestPair(1);
+        ClosestPair.Location point = cp.buildLocation(3.0, 4.0);
+        assertNotNull(point);
+        assertEquals(3.0, point.x);
+        assertEquals(4.0, point.y);
+    }
+
+    @Test
+    public void testCreateLocation() {
+        ClosestPair cp = new ClosestPair(5);
+        ClosestPair.Location[] locations = cp.createLocation(5);
+        assertNotNull(locations);
+        assertEquals(5, locations.length);
+    }
+
+    @Test
+    public void testXPartition() {
+        ClosestPair cp = new ClosestPair(5);
+        ClosestPair.Location[] points = new ClosestPair.Location[5];
+        points[0] = cp.buildLocation(2.0, 3.0);
+        points[1] = cp.buildLocation(5.0, 1.0);
+        points[2] = cp.buildLocation(1.0, 6.0);
+        points[3] = cp.buildLocation(4.0, 7.0);
+        points[4] = cp.buildLocation(3.0, 2.0);
+
+        int pivotIndex = cp.xPartition(points, 0, 4);
+        assertEquals(2, pivotIndex);
+        assertEquals(2.0, points[0].x);
+        assertEquals(1.0, points[1].x);
+        assertEquals(3.0, points[2].x);
+        assertEquals(4.0, points[3].x);
+        assertEquals(5.0, points[4].x);
+    }
+
+    @Test
+    public void testYPartition() {
+        ClosestPair cp = new ClosestPair(5);
+        ClosestPair.Location[] points = new ClosestPair.Location[5];
+        points[0] = cp.buildLocation(2.0, 3.0);
+        points[1] = cp.buildLocation(5.0, 1.0);
+        points[2] = cp.buildLocation(1.0, 6.0);
+        points[3] = cp.buildLocation(4.0, 7.0);
+        points[4] = cp.buildLocation(3.0, 2.0);
+
+        int pivotIndex = cp.yPartition(points, 0, 4);
+        assertEquals(1, pivotIndex);
+        assertEquals(2.0, points[1].y);
+        assertEquals(3.0, points[4].y);
+        assertEquals(1.0, points[0].y);
+        assertEquals(6.0, points[2].y);
+        assertEquals(7.0, points[3].y);
+    }
+
+    @Test
+    public void testBruteForce() {
+        ClosestPair cp = new ClosestPair(2);
+        ClosestPair.Location loc1 = cp.buildLocation(1.0, 2.0);
+        ClosestPair.Location loc2 = cp.buildLocation(4.0, 6.0);
+
+        ClosestPair.Location[] locations = new ClosestPair.Location[] {loc1, loc2};
+        double result = cp.bruteForce(locations);
+        assertEquals(5.0, result, 0.01);
+    }
+}