Computer program testing after source code for the computer program has been modified is performed more quickly, by using execution conditions. First, second, and third execution conditions are determined. These execution conditions are used to perform testing of the program to determine whether the program is properly functioning. Particularly, test data on which basis testing of the computer program is performed can be classified as first test data, second test data, third test data, or fourth test data. The program prior to modification of the source code is tested by employing the first, second, and third test data. After the source code is modified, the program is retested by employing only the third and the fourth test data. The program is thus properly retested after source code modification by employing only the third and the fourth test data, without having to employ the first and the second test data.