When running a step with credentials and powershell, powershell does not retrieve the variables properly, shows as empty / null.  In the same step, using batch function, the variable shows.

steps {
withCredentials([string(credentialsId: 'testvar', variable: 'test')])

{ powershell 'echo "This is a $test"' bat 'echo "This is a %test%"'   }

}