Definition of test: The purpose of program testing is to implement a process of the program in order to find errors. The task and purpose of testing can be expressed as:purpose: to find errors in the program;task: to find hidden errors in the program by running the program on the computer.Another term related to prediction is called debugging. Its purpose and tasks can be specified as:purpose: to find and correct errors;task: to eliminate software failures, so as to ensure the reliable operation of the program. The relationship between testing and error correction can be illustrated with the data flow diagram in Figure 6-1. It can be seen from the figure that each test of the system is to prepare several test data, so as to be sent into the computer together with the tested program for command execution. Generally, we call the test data required for program execution once as a "Test Case". Each test case produces a corresponding "test result". But if its test result is not consistent with the "expected result" , That is to say that there is an error in the program, we need to find and correct it.