JUnit中如何测试异常

import junit.framework.TestCase;

public class TestEmailAddrValidator extends TestCase {
    EmailAddrValidator validator = new EmailAddrValidator();

    public void testDoValidate() throws ValidationException {
        validator.doValidate("glchengang@163.com", null);
        validator.doValidate("glchen.gang@163.com", null);
        validator.doValidate("glchen_gang@163.com", null);
        validator.doValidate("glchen.gang@163_tom.com", null);
    }

    public void testDoValidateException() {
        testDoValidateException("@b.c");
        testDoValidateException("a@.c");
        testDoValidateException("a@b.");
        testDoValidateException("@.c");
        testDoValidateException("@...");
        testDoValidateException(" ");
        testDoValidateException(null);
    }

    private void testDoValidateException(String email) {
        try {
            validator.doValidate(email, null);
            fail("末抛出异常");
        } catch (ValidationException e) {
            assertTrue(true);
        }
    }
}

import java.util.Locale;
import com.hygensoft.common.configure.ConfigureObject;

public class EmailAddrValidator{

    protected static final String ERROR_CODE_INVALID_EMAIL_ADDR = "INVALID_EMAIL_ADDR";
    protected static final String ERROR_CODE_INVALID_INPUT = "INVALID_INPUT_OBJECT";

    public Object doValidate(Object input, Locale locale) throws ValidationException {
        if (!(input instanceof String)) {
            throw new ValidationException(ERROR_CODE_INVALID_INPUT, input);
        }
        String inputStr = (String) input;
        int idx = inputStr.indexOf('@');
        if (idx == -1 || idx == 0) {
            throw new ValidationException(ERROR_CODE_INVALID_INPUT, input);
        }
        int idx2 = inputStr.indexOf('.', idx);
        if (idx2 == -1 || idx2 == idx + 1) {
            throw new ValidationException(ERROR_CODE_INVALID_INPUT, input);
        }
        if (inputStr.endsWith(".")) {
            throw new ValidationException(ERROR_CODE_INVALID_INPUT, input);
        }
        return input;
    }

    /* (non-Javadoc)
     * @see com.hygensoft.common.configure.Configurable#initialize(com.hygensoft.common.configure.ConfigureObject)
     */
    public void initialize(ConfigureObject conf) {}

}