1. A method for editing and testing computer programming code, the method comprising: receiving, by one or more computer processors, a first file comprising computer programming code; receiving, by one or more computer processors, a code overlay comprising one or more modifications to be applied to the computer programming code of the first file; determining, by the one or more computer processors, a first location within the computer programming code of the first file, at which to apply the code overlay; generating, by one or more processors, a second file comprising uncompiled composite computer programming code, wherein the uncompiled composite computer programming code includes the computer programming code of the first file modified by the one or more modifications of the code overlay applied at the first location; and executing, by one or more computer processors, the uncompiled composite computer programming code of the second file to test the uncompiled composite computer programming code of the second file.