新手请教用junit 测试JAVA类遇到的问题,请高手指点一下 有点小郁闷

我是个新手,刚学习了点JUINT,现练习写个测试类,但是遇到问题了,不知道错在哪里,请师傅指点一二.
JAVA原类如下:

package test;
public class YY {
public static void main(String[] args)
{
YY e = new YY();
e.printIt("One, ")
.printIt("Two, ")
.printIt("Three, ");
}

public YY printIt(String s)
{
System.out.print(s);
  return this;
}
}
测试类如下"
package test;

import junit.framework.TestCase;

public class YYTest extends TestCase {
         public YY y1;       
         public String s;
       

        protected void setUp() throws Exception {
                super.setUp();
                y1=new YY();
               
               
        }
       

        protected void tearDown() throws Exception {
                super.tearDown();
        }
public void printItTest() throws Exception
{
        assertEquals("one",y1.printIt(s));
}
public static void main(String[] args) {
        junit.textui.TestRunner.run(YYTest.class);
}
}
在ECLIPSE下运行,错误提示如下:
junit.framework.AssertionFailedError: No tests found in test.YYTest
        at junit.framework.Assert.fail(Assert.java:47)
        at junit.framework.TestSuite$1.runTest(TestSuite.java:93)
        at junit.framework.TestCase.runBare(TestCase.java:130)
        at junit.framework.TestResult$1.protect(TestResult.java:110)
        at junit.framework.TestResult.runProtected(TestResult.java:128)
        at junit.framework.TestResult.run(TestResult.java:113)
        at junit.framework.TestCase.run(TestCase.java:120)
        at junit.framework.TestSuite.runTest(TestSuite.java:228)
        at junit.framework.TestSuite.run(TestSuite.java:223)
        at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:478)
        at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:344)
        at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:196)

junit.framework.AssertionFailedError: No tests found in test.YYTest
        at junit.framework.Assert.fail(Assert.java:47)
        at junit.framework.TestSuite$1.runTest(TestSuite.java:93)
        at junit.framework.TestCase.runBare(TestCase.java:130)
        at junit.framework.TestResult$1.protect(TestResult.java:110)
        at junit.framework.TestResult.runProtected(TestResult.java:128)
        at junit.framework.TestResult.run(TestResult.java:113)
        at junit.framework.TestCase.run(TestCase.java:120)
        at junit.framework.TestSuite.runTest(TestSuite.java:228)
        at junit.framework.TestSuite.run(TestSuite.java:223)
        at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:478)
        at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:344)
        at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:196)

这是怎么回事呀,我的测试类写的一定有问题吧,应该怎么样写呀