adding test stage

Jenkinsfile

@@ -11,5 +11,20 @@
                 sh 'python -m py_compile sources/add2vals.py sources/calc.py' 
             }
         }
+      stage('Test') {
+             agent {
+                 docker {
+                     image 'qnib/pytest'
+                 }
+             }
+             steps {
+                 sh 'py.test --verbose --junit-xml test-reports/results.xml sources/test_calc.py'
+             }
+             post {
+                 always {
+                     junit 'test-reports/results.xml'
+                 }
+             }
+         }
     }
-}
+}