I am trying to set up a development environment for KDE running Stretch. I have been attempting to use the kdesrc-build tool to build okular but each time I run it cmake fails to build the package. When I looked into the cmake log file, I found that cmake fails because okular is requesting a qt config file for a qt version of at least 5.8.0 but my system has only 5.7.1. I looked some more into it and found that an updated version is found in the qtbase5-dev package from the testing repository.
Here is my question: How can I set up my system to develop KDE software without messing up my installation of Debian?