Bugs & Debugging - Testing

1. 10 Bugs & Debugging - Testing

2. Previously • Design a program • Break the problem into smaller ones • It may help to do it several times to reduce the problem enough • Outlines • Javadoc • Industry standard for documenting Java code • Create documentation in HML format • Other format can be obtained

3. Overview • Types of Errors • When errors appear • Compiler Errors • Run-time errors • Fixing errors • Testing - Find Errors

4. Types of Errors • Syntax errors • Code that does not conform to the syntax of the programming language • Detected a compiling time // Declaring variables intiCounter = 0 intiValue; iValue = ++iCounter; 1 2 3 4 5

5. Types of Errors • Semantic errors • Mistakes in the logic of the code • Legal language code but not what intended • Appear when running the code • Exceptions

6. When errors appear • Compile-time errors • Appear when the code is compiled • Run-time errors • Appear when the code is running • Makes the code to behave different than expected • Could take long time before effects are seen • Logical errors are run-time errors • Some languages try to reduce the risk of this errors, Java is one of them

7. Compiler Errors • Eclipse will show them with a read circle and a cross • Some information is provided • The point of the error may not be where the error was introduced • Unbalanced braces cannot be detected until the braces are closed – indexation helps to detect the point of the problem • Previous error may create other errors, “spurious” errors

8. Compiler Errors Let see some using Eclipse!

9. Run-time errors • Java does not allow some code to avoid potential run-time errors float fCostProduct1 = 12.50; float fCostProduct2 = 30.10; int iTotal = fCostProduct1 + fCostProduct2; • Potential run-time errors may be detected by Eclipse and are displayed with a yellow triangle with an exclamation mark • You should investigate them • Take the appropriate action to remove them

10. Run-time errors • Cause: Lack of validation • An example would be when expected a number and provided a string • Remember the exercise to convert from Celsius to Fahrenheit the data is inputted as an string from the console and converted to a number • What happen if the user input a character not a digit? • An exception is thrown

11. Run-time errors RuntimeException ArithmeticException e.g. 10 / 0 NullPointerException IndexOutOfBoundsException ...

12. Run-time errors Other causes: • External factors • Out of memory • Insufficient i/o privileges ... • Internal factors • Arithmetic errors • Invalid operation, e.g. try to read beyond the end of a file • Try to access an object that doesn’t exist, e.g. null object • Attempt to read beyond the end of an array ...

13. Run-time errors • Logical errors • Causes a program to operate incorrectly • The program does not terminate abnormally or crash • The behaviour of the program is different that what was intended • Can be difficult to spot

14. Run-time errors 1 2 3 4 5 6 7 8 9 10 11 12 // Example of a logical error String strAnswer; System.out.println("Press 'y' to continue or any other key” + ” to terminate: "); strAnswer = Scanner.nextLine(); // Exit the program if the key 'y' is pressed if (strAnswer.charAt(0) == 'n') { // Terminate the application System.exit(0); } ...

15. Run-time errors Let see some using Eclipse!

16. Fixing errors • Need to know an error exists – find errors • Gather as much information as possible • Logging messages helps • Establish where the error happens in the code • Debugging is the process of locating the errors (bugs) in the code • Design the fix • Implement the fix • Test that the fix really fixes the problem

17. Run-time errors Let do some debugging using Eclipse!

18. Testing - Find Errors • Test to find errors (bugs) that may exist in the code • Different type of tests are conducted at different stages of a project • Tests intend to establish the compliance to the requirements • Errors should be reproducible! • Requirement to be able to locate them and fix • Information gathered required to reproduce it

19. Testing - Find Errors • Create unit testing • Test units of your code • Check if the unit does what it is expected • The units are methods • Use JUnit in Java • Run some simple examples • System test • Test the complete, integrated system to evaluate the compliance of the system – behave as expected • Customers – NOT GOOD