Do the terms of the GPL apply to an application if the open-sourced code it incorperates only exists in debug (internal-use only) versions of the software?
For example, I take a GPL unit testing framework and build that into my closed source application. I conditionally include this code ONLY in a special build of the software used internally. For distributed binary versions, this code is ignored. (you know, #ifdef-ed away).
If the code never ends up in the distributed binaries you are free to use GPL libraries. You can even use GPL code in your closed source and self hosted web platform as long as you don't give it away :)
But be kind and give the author of the library you are using something in return, such as patches or kind thanks :)
Fom the GPL FAQ:
Is making and using multiple copies within one organization or company “distribution”?
No, in that case the organization is just making the copies for itself. As a consequence, a company or other organization can develop a modified version and install that version through its own facilities, without giving the staff permission to release that modified version to outsiders. However, when the organization transfers copies to other organizations or individuals, that is distribution. In particular, providing copies to contractors for use off-site is distribution.
The GPL is not an EULA, it is a distribution license. If you're not distributing code (source or binary), then it cannot apply to you.
I agree with @Armin, but would add one thought: be sure that "internal-only" is really internal only. You can trip into distribution if your company uses outside contractors for some role in the development process or, for example, you do joint testing with a customer.