Jenkinsfile does not take into account conditional on branch - jenkins

Question

Here are the stages of my Jenkinsfile
stages {
stage("build") {
when {
expression {
BRANCH_NAME = 'alerta_dev_infra'
}
}
steps {
echo 'buidling the webhook'
}
}
stage("test") {
when {
expression {
env.BRANCH_NAME = 'alerta*'
}
}
steps {
echo 'testing the webhook'
}
}
stage("deploy") {
when {
expression {
env.BRANCH_NAME = 'alerta_dev_infra'
}
}
steps {
echo 'deploying the webhook'
}
}
}
However, when it is executed:
14:10:00 Push event to branch alerta_dev_infra
14:10:00 Started by user pkaramol#foo.bar
14:10:00 Rebuilds build #9
14:10:49 First time build. Skipping changelog.
14:10:49 [Pipeline] }
14:10:49 [Pipeline] // stage
14:10:49 [Pipeline] withEnv
14:10:49 [Pipeline] {
14:10:49 [Pipeline] container
14:10:49 [Pipeline] { (hide)
14:10:49 [Pipeline] stage
14:10:49 [Pipeline] { (build)
14:10:49 Stage "build" skipped due to when conditional
14:10:49 [Pipeline] }
14:10:50 [Pipeline] // stage
14:10:50 [Pipeline] stage
14:10:50 [Pipeline] { (test)
14:10:50 Stage "test" skipped due to when conditional
14:10:50 [Pipeline] }
14:10:50 [Pipeline] // stage
14:10:50 [Pipeline] stage
14:10:50 [Pipeline] { (deploy)
14:10:50 Stage "deploy" skipped due to when conditional
14:10:50 [Pipeline] }
14:10:50 [Pipeline] // stage
14:10:50 [Pipeline] }
14:10:50 [Pipeline] // container
14:10:50 [Pipeline] }
14:10:50 [Pipeline] // withEnv
14:10:50 [Pipeline] }
14:10:50 [Pipeline] // node
14:10:50 [Pipeline] }
14:10:50 [Pipeline] // podTemplate
14:10:50 [Pipeline] End of Pipeline

Answer 1

This worked for me
when {
expression {
return env.GIT_BRANCH == "origin/master"
}
}

Answer 2

I have used the Choice Parameter to provide three choices for branch to select: master, develop and feature-1
Here is the pipeline code to use when conditional on BRANCH_NAME parameter
pipeline {
agent any
stages {
stage ('Build in master') {
when {
expression { params.BRANCH_NAME == 'master' }
}
steps {
echo "Building in master"
}
}
stage ('Build in develop')
{
when {
expression { params.BRANCH_NAME == 'develop' }
}
steps {
echo "Building in develop"
}
}
stage ('Build in feature')
{
when {
expression { params.BRANCH_NAME == 'feature-1' }
}
steps {
echo "Building in feature-1"
}
}
}
}
Output of the pipeline job: