如何编写自定义的Spock交互mini-DSL来测试我的邮件发送？

import spock.lang.*
import javax.mail.*

class EmailSender {
    def sendEmail(String to, String subject, String body) {
        // 实际的邮件发送逻辑
    }
}

class EmailSenderSpec extends Specification {
    @Subject
    EmailSender emailSender = new EmailSender()

    def "should send email successfully"() {
        given:
        givenEmailServerUp()

        when:
        emailSender.sendEmail("test@example.com", "Hello", "This is a test email")

        then:
        noExceptionThrown()
    }

    def "should handle email server down"() {
        given:
        givenEmailServerDown()

        when:
        emailSender.sendEmail("test@example.com", "Hello", "This is a test email")

        then:
        thrown(MessagingException)
    }

    def givenEmailServerUp() {
        // 模拟邮件服务器可用的情况
    }

    def givenEmailServerDown() {
        // 模拟邮件服务器不可用的情况
    }
}