Add unit test for ClosestPairOfPoints class

Author: sandeepgoudmacha

src/test/java/com/thealgorithms/geometry/closestPairOfPointsTest.java

@@ -0,0 +1,18 @@
+package com.thealgorithms.geometry;
+
+import static org.junit.jupiter.api.Assertions.*;
+import java.util.Arrays;
+import org.junit.jupiter.api.Test;
+
+public class ClosestPairOfPointsTest {
+    @Test
+    void testClosestPair() {
+        var pts = Arrays.asList(
+            new Point(2, 3), new Point(12, 30),
+            new Point(40, 50), new Point(5, 1),
+            new Point(12, 10), new Point(3, 4)
+        );
+        double result = ClosestPairOfPoints.closestPair(pts);
+        assertEquals(Math.sqrt(2), result, 1e-6);
+    }
+}