In one embodiment, a method for editing and testing computer programming code is provided. The method includes receiving a first file comprising computer programming code, and a first code overlay comprising one or more modifications to be applied to the computer programming code of the first file. The method further includes determining a first location within the computer programming code of the first file, at which to apply the first code overlay. The method further includes generating a second file comprising uncompiled composite computer programming code, the uncompiled composite computer programming code comprising the computer programming code of the first file modified by the one or more modifications applied at the first location. The method further includes testing the uncompiled composite computer programming code of the second file.