def notify_success() {
    slackSend color: "good", message: "${env.JOB_NAME} #${env.BUILD_NUMBER} succeeded! (<${env.RUN_DISPLAY_URL}|Open>)"
}

def notify_failure() {
    slackSend color: "danger", message: "${env.JOB_NAME} #${env.BUILD_NUMBER} failed! Check the status (<${env.RUN_DISPLAY_URL}|here>)."
}

pipeline {
    agent any 
        
    stages {
        stage('first test'){
            steps{
                ...
            }
        }
        stage('testing'){
            steps{
                ...
                if (currentBuild.result == "SUCCESS") {
                    notify_success()
                } else {
                    notify_failure()
                }
            }
        }
    }
}