Added basic test class for class LinkedList

src/test/java/io/ad/structs/LinkedListTest.java

+package io.ad.structs;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+//TODO Complete Test class.
+public class LinkedListTest {
+
+    LinkedList<Integer> testList;
+
+    @BeforeEach
+    void setup() {
+        testList = new LinkedList<>();
+        testList.add(0);
+        testList.add(1);
+        testList.add(2);
+    }
+
+    @Test
+    void testCreateEmptyList() {
+        LinkedList<Integer> emptyList = new LinkedList<>();
+        assertEquals(0, emptyList.size());
+    }
+
+    @Test
+    void testSize() {
+        int currentSize = testList.size();
+        testList.add(3);
+        assertEquals(currentSize+1, testList.size());
+    }
+    
+}
\ No newline at end of file