/**
 * Runs npm test inside current container. Expects npm install already done.
 * Must be called inside container('node') block.
 *
 * config keys (all optional):
 *   workDir  - directory to run in, default: '.'
 *   testCmd  - npm script to run, default: 'test'
 */
def call(Map config = [:]) {
    def workDir = config.workDir ?: '.'
    def testCmd = config.testCmd ?: 'test'

    dir(workDir) {
        sh "npm ${testCmd}"
    }
}