Add KNNTest class for KNN classification testing

Author: Rajat-Builds

src/main/java/com/thealgorithms/machinelearning/KNNTest.java

@@ -0,0 +1,20 @@
+package com.thealgorithms.machinelearning;
+
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class KNNTest {
+    @Test
+    public void testClassifyStandard() {
+        List<KNN.DataPoint> dataset = new ArrayList<>();
+        dataset.add(new KNN.DataPoint(new double[] {1.0, 1.0}, "GroupA"));
+        dataset.add(new KNN.DataPoint(new double[] {1.5, 2.0}, "GroupA"));
+        dataset.add(new KNN.DataPoint(new double[] {8.0, 9.0}, "GroupB"));
+
+        double[] target = new double[] {1.2, 1.3};
+        String result = KNN.classify(dataset, target, 2);
+        Assertions.assertEquals("GroupA", result);
+    }
+}