Basic structure of graph for testing

NodeBasedTests.java

import sun.awt.image.ImageWatched;

import java.util.Iterator;
import java.util.LinkedList;

public class NodeBasedTests {
    public static void main(String[] args) {
        PartA partA = new PartA();
        PartB partB = new PartB();
        PartC partC = new PartC();
        PartD partD = new PartD();
        PartE partE = new PartE();
        PartF partF = new PartF();

        TestGraph testGraph = new TestGraph();
        testGraph.addVertex(partA);
        testGraph.addVertex(partB);
        testGraph.addVertex(partC);
        testGraph.addVertex(partD);
        testGraph.addVertex(partE);
        testGraph.addVertex(partF);

        testGraph.addEdge(partA, partD);
        testGraph.addEdge(partB, partD);
        testGraph.addEdge(partB, partC);

        System.out.println();
        testGraph.printConnected(partA);
        System.out.println();
        testGraph.printConnected(partB);
    }
}

class TestGraph {
    private LinkedList<LinkedList<TestComponent>> testComponents = new LinkedList<>();

    public void addVertex(TestComponent vertex) {
        LinkedList<TestComponent> vertexList = new LinkedList<>();
        vertexList.add(vertex);
        testComponents.add(vertexList);
    }

    public void addEdge(TestComponent source, TestComponent dest) {
        LinkedList tmp;
        Iterator iterator = testComponents.iterator();
        while (iterator.hasNext()) {
            tmp = (LinkedList) iterator.next();
            if (tmp.getFirst().getClass().isInstance(source)) {
                System.out.println(source.getClass());
                tmp.add(dest);
                break;
            }
        }
    }

    public void printConnected(TestComponent vertex) {
        LinkedList tmp;
        Iterator iterator = testComponents.iterator();
        while (iterator.hasNext()) {
            tmp = (LinkedList) iterator.next();
            TestComponent first = (TestComponent) tmp.getFirst();
            if (first.getClass().isInstance(vertex)) {
                Iterator vertexIterator = tmp.iterator();
                while (vertexIterator.hasNext()) {
                    TestComponent v = (TestComponent) vertexIterator.next();
                    System.out.println(v.getClass());
                }
                break;
            }
        }
    }
}

interface TestComponent {
    public void nowTesting();
}

class PartA implements TestComponent {
    @Override
    public void nowTesting() {

    }
}

class PartB implements TestComponent {
    @Override
    public void nowTesting() {

    }
}

class PartC implements TestComponent {
    @Override
    public void nowTesting() {

    }
}

class PartD implements TestComponent {
    @Override
    public void nowTesting() {

    }
}

class PartE implements TestComponent {
    @Override
    public void nowTesting() {

    }
}

class PartF implements TestComponent {
    @Override
    public void nowTesting() {

    }
}