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; receiving, by one or more processors, a first input that identifies one or more lines of computer programming code within the first file; determining, by one or more processors, one or more offset values corresponding to the identified one or more lines of computer programming code of the first file; creating, by one or more processors, another code overlay based, at least in part, on identified one or more lines of computer programming code and the corresponding one or more offset values associated with the identified one or more lines of computer programming code of the first file; receiving, by one or more processors, a second input that identifies a storage location of the other code overlay; and storing, by one or more processors, the other code overlay within the storage location of the second input; 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.