If you created the project as an IDEA Platform Plugin project, the proper run/debug configuration should already be present in the Run/Debug Configurations drop down. Otherwise, if you decided to start from the Java project, you will need to define the run/debug configuration on your own. Refer to the Running your project section of Chapter 5, Make It Happen – Running Your Project, for information on how to create a runtime or debug configuration.
When developing plugins, the required profile type is Plugin, as shown here:
Running or debugging a configuration profile defined in this way will spawn a second instance of IntelliJ.
Tip
When running the plugin development run/debug configuration for the first time, a completely new instance of IntelliJ IDEA will be started, complete with its own set of settings. A few dialog boxes will pop up asking you to import settings or enter your license. Don't worry, it will not overwrite your base IntelliJ IDEA installation settings...