Testing and Validating program

Programming errors Debugging – is the process of finding and

correcting errors in computer programs.Program debugging is another form of

problem solving.3 types of programming errors:

Design errorsSyntax errorsRun-time errors

Design errorsOccurs during :

AnalysisDesignImplementation

phases

•Make mistake in translating an algorithm into program •Choose incorrect method of solution for the problem to be solved•Design erroneous data for the program.

Difficult to detect Debugging process: review careful the problem analysis , algorithm design , test data

Syntax errors/compilation errorsViolation of syntax rulesSyntax rules – define how the elements of a

programming language must be writtenOccur during the implementation phase –

detected by compiler during compilation process

Compiler issues diagnostic message-warning message/error message

continueWarning message

Indicates a minor error that may lead to a problem during program execution.

Does not cause the termination of the compilation process.

May cause errors sometimes (if serious)…It is a good practice to warning seriously and

eliminate their causes in the program.

continueError message

Will cause the compiler stop from compiling the program

It tell that nature of the errors and the location of errors in the program

Since compiler explicitly ‘inform” the errors, thus syntax errors is relatively easy

Example: syntax error >>> while True print 'Hello world‘ File "<stdin>", line 1, in ? while True print 'Hello world' ^ SyntaxError: invalid syntax

continueThe parser repeats the offending line and

displays a little ‘arrow’ pointing at the earliest point in the line where the error was detected.

The error is caused by (or at least detected at) the token preceding the arrow: in the example, the error is detected at the keyword print since a colon (':') is missing before it.

File name and line number are printed so you know where to look in case the input came from a script.

Example 2 >>> print a+b:

SyntaxError: invalid syntax

Run-times errorsDetected by computer while your program is

being executed.They are cause by program instructions that

require the computer to do something illegal such as attempting to store inappropriate data or divide a number by 0.

When a run-time error is encountered, the computer produces an error diagnostic message and terminates the program execution.

Example: run-time errors>>> print 1/0

Traceback (most recent call last): File "<pyshell#6>", line 1, in <module> print 1/0ZeroDivisionError: integer division or modulo

by zero

Example 2>>> list=[123,'abc']>>> print list[1]abc>>> print list[2]Traceback (most recent call last): File "<stdin>", line 1, in <module>IndexError: list index out of range

Testing and verification Program verification- is the process of

ensuring that a program meets user requirements

Technique that can be use to verify program is by using program testing.

What is program testing???? program testing is the process of executing a

program to demonstrate its correctness.

continueUsed a set of data to test your programCorrected output not necessarily means your

program is logically correct.??? Why???Must test all the conditions (if any) ,

selection, looping all must be tested to look at the flow …logic or not…

Data validationIn computer science data validation is the

process of ensuring that a program operates on clean, correct and useful data.

It uses routines, often called “validation rules " or "check routines", that check for correctness, meaningfulness, and security of data that are input to the system.

Visual Studio .NET 2003

exampleThe simplest data validation verifies that the

characters provided come from a valid set. For example, telephone numbers should

include the digits and possibly the characters +, -, (, and ) (plus, minus, and brackets).

A more sophisticated data validation routine would check to see the user had entered a valid country code, i.e., that the number of digits entered matched the convention for the country or area specified.

Visual Studio .NET 2003