fix: add simple example

TESTING.md

@@ -3,3 +3,44 @@
 Testing is a project specific concern. That being said, each project may use a jenkins pipeline to setup CI and CD for the project.
 
 We use [jenkins-vagrant](https://github.com/etclabscore/jenkins-vagrant)
+
+Here is an example jenkins file that runs node project tests in each of osx, linux and windows:
+
+```yaml
+pipeline {
+  agent none
+  stages {
+    stage('Run Tests') {
+      parallel {
+        stage('test') {
+	        agent {
+            label 'macos'
+          }
+          steps {
+              sh 'npm install'
+              sh 'npm test'
+          }
+        }
+        stage('linux') {
+          agent {
+            label 'linux'
+          }
+          steps {
+            sh 'npm install'
+            sh 'npm test'
+          }
+        }
+        stage('windows') {
+          agent {
+            label 'windows'
+          }
+          steps {
+            bat 'npm install'
+            bat 'npm test'
+          }
+        }
+      }
+    }
+  }
+}
+```