VALIDATION AND ERROR HANDLING

1. VALIDATION AND ERROR HANDLING

2. During the development and use of software there are many opportunities for different types of error to creep in. • Every programmer should remember the famous acronym GIGO • Garbage In, Garbage Out. • This means that your program cannot possibly produce the correct results if the input data is invalid. There are several reasons for invalid input data: • The user mistypes a value. • The user types a value in the wrong format. • The user uses a value meant for another input. • The user misunderstands what data the program expects. • Careful checks are essential so that the data is as accurate as possible. A variety of cheques have been devised to minimise the possibility of invalid data.

3. VALIDATION • Validation Checks • Range Checks • Format Checks • Length Checks • Type Checks • Lookup Checks • Check Digits • Presence Checks

4. TESTING However carefully you design and code your program, it is very unlikely it will work perfectly first time round. The longer the source code of the programme, the more errors there are likely to be. Good program layout, a modular approach and good use of routines with interfaces and local variables will improve your chances of debugging your program however; we cannot be certain that a large programme will never malfunction. No testing devised so far can prove the program works under all circumstances, the bigger a piece of software, the more likely it is that it may fail sometime. Testing can only reveal the presence of errors. Thorough testing can provide us with some assurance that we have a robust system.

5. TESTING STRATEGIES • Dry-run testing • Black box testing • White box testing

6. SELECTION OF TEST DATA • Normal Data • Boundary Data • Erroneous Data