Could not find the TestPlan class

JMeter Error in NonGUIDriver java.lang.Runtime Exception : Could not find the TestPlan class!

Sometime when developing your scripts in the JMeter GUI you will update and modify items within the WorkBench pictured below.​

This workbench acts as a temporary work space and is not intended for JMeter's headless mode. By default, the workbench is not automatically saved with the test plan, but it can be saved by checking "Save Workbench" option on Workbench element.

If you try to run the test plan on Flood you will see the following error in your logs.

JMeter Error in NonGUIDriver java.lang.Runtime Exception : Could not find the TestPlan class!
at org.apache.jmeter.engine.StandardJMeterEngine.configure(StandardJMeterEngine.java:162)
at org.apache.jmeter.NewDriver.main(NewDriver.java:259)
Error in NonGUIDriver java.lang.Runtime Exception : Could not find the TestPlan class!
at org.apache.jmeter.JMeter.start(JMeter.java:504)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at org.apache.jmeter.JMeter.startNonGui(JMeter.java:879)
at org.apache.jmeter.JMeter.runNonGui(JMeter.java:944)

To solve this, simply move your test items from the Workbench to the Test Plan element.