Design the Test Plan Workflow

Go to Jira Administration > Issues > Workflow and design the workflow. 

Here is a simple example that can be used as a Test Workflow. 

Recommendations

• Have an initial status (e.g., “new”), another when it’s in progress (e.g., “in progress”), and then another when it’s finished (e.g., “closed”).
• You may need to have an interim status if you need to review the results of a Test Plan.

Update the Workflow Scheme 

After designing the workflow you need to make it active for your project, you do that by updating the workflow scheme.

Go to your Project > Project settings > Workflows and click  "Add Workflow.  

Then select the workflow and mapped it with the issue type Test Plan:

Don't forget to publish the scheme after updating!

Want to know more about creating and configuring workflows? Check out the Atlassian Documentation.