1. A computer-implemented method comprising: in response to an input to a graphic-based programming tool which is used to build a screen and generate underlying screen program logic concurrently, automatically placing a block of reusable test code corresponding to the input into a test script file, wherein the block of reusable test code causes the graphic-based programming tool to build the screen or to write the underlying screen program logic, and wherein the test script file includes blocks of reusable test code and commands the graphic-based programming tool to automatically simulate building of the screen or writing of the underlying screen program logic; automatically placing parameter data corresponding to the input into a data file which is separated from the test script file, wherein the parameter data include properties of an item on the screen that when linked to a block of reusable test code in the test script file, cause the graphic-based programming tool to build the item on the screen or write the underlying screen program logic; and linking the data file with the test script file to test the input.