cores.groovy

def call() {
  // Runtime.runtime.availableProcessors()
  def value = sh(returnStdout: true, script: 'nproc')
  value = value.trim()
  return value.toInteger()
}

MachineThreading.jenkins

def execute() {
  node('master') {
    stage ('Checkout') {
      checkout scm
    }
    stage ('Cores') {
      cores()
    }
  }
}

return this

TestMachineThreading.groovy

import static com.lesfurets.jenkins.unit.MethodSignature.method
import com.lesfurets.jenkins.unit.BasePipelineTest
import org.junit.Test
import org.junit.Before

class TestMachineThreading extends BasePipelineTest {
  @Override
  @Before
  void setUp() throws Exception {
    super.setUp()
  }

  @Test
  void available_cores_returned() throws Exception {
    try {
      def script = loadScript('src/test/resources/MachineThreading.jenkins')
      script.execute()
      printCallStack()
    }
    catch (MalformedURLException ex) {
      // Do nothing.
    }
  }
}