I think that could be what caused it. What's the name of the directory where Screenshot.py is located? You could try searching for the name +test on your file system and see if the image shows up. For example if the file is saved in a directory named "NewGC" the image saved should be named "NewGCtest.png". Try checking if the image wasn't saved in the directory above where your folder is. Like if the folder where you saved the files is located in your Documents folder, check if the image wasn't saved there.
Let me know if there's anything else I can help with