Debugging Oracle BPM has been a bit tedious. One would often start setting logmessages which will clutter your logs when running the project in a production environment (and a performance issue when not needed!)
This post contains several ways of debugging;

1. Debug in BPM Studio
2. Debug BPM Methods
3. logMessage(s) with simple types
4. logMessage(s) with complex types

Debug in BPM Studio:

1. First toggle a breakpoint in your code. (Right mouse click on the left side of your code)
2. Then click “Open Debug Dialog” in the menu “Run”:
3. 
4. Create a new “BPM Process Debugger” by clicking on “New launch configuration”
5. 
6. Give the configuration a name
7. Select the project
8. Click Apply and then Debug button
9. Run your project until it reaches your breakpoint:
   

Debug BPM Methods

1. Select the BPM Script Launcher and click New Launch Configuration
2. Choose the project
3. Type the component name
4. Choose the method
5. Click Apply and debug
6. Remember that the method values needs to be initialized.

logMessage(s) with simple types:

You can log simple types by using the logMessage command:

logMessage("<< [" + process.name + "] [" + Activity.name + "] " + "message received but not for this process\nMessage contents: " + message.textValue, severity : Severity.WARNING);

This would result in a warning log statement with message being displayed.

logMessage(s) with complex types:

A quick way to display complex types is through DynamicXml, which will take bpm variables (complex & simple).

logMessage("complexTypeVariable:\n" + DynamicXml.createXmlTextFor(object : complexTypeVariable)

This is an example of the log statement:

complexTypeVariable:
<xobject.Src.Com.Joris.BPM.Types.complexTypeVariable xmlns="http://bea.com/albpm/DynamicXml/version/2.0">
	<firstvalue>123</firstvalue>
	<secondvalue>second</secondvalue>
	<thirdvalue>false</thirdvalue>
</xobject.Src.Com.Joris.BPM.Types.complexTypeVariable>

I’ll expand this post in the future with (Process) Unit tests as well.
Happy debugging!