Programming

Types of Testing

Lesson Objectives

• Review and understand the concept of testing and debugging a program.

• Review the concept of a dry run test.

• Understand the concept of a trace table.

• Perform try run tests using trace tables.

Test and debug the program

• Testing is performed by a tester or

end user

– to find bugs, faults or error in the

program.

• The tester reports to the

programmer or program

development team.

Types of Testing• There are two types of testing:

– A dry –run test

involves applying test data to the program

manually and tracing the logic or reasoning

of the program using test data that will test

each section of the program.

– This can even be done before the

algorithm is translated into the

programming language.

Types of testing• Computer testing

– Compile the program. • A computer can only execute a program

written in machine language. • Before the computer can run the Pascal

program, the latter must be converted to machine language.

• The source code must be converted into machine language. The program which does this is a compiler.

• The compiler will check for errors in the program. e.g syntax errors

Types of testing

• What are some types of syntax errors in Lazarus?– Omitting

• ;• ,• ‘• ()

– i.e. any violation of syntax rules

Types of testing• Run the program.

– The user requests the computer to execute the

program and the user supplies data to the program

for which he or she knows the answer.

– Such data is called test data.

– If the program does not give the correct answers

the user knows that the program has at least one

logic error.

– If the program contains logic errors we must debug

the program; find and correct those errors.

Types of testing

• Debugging is the process of fixing the

errors found by the testers.

NB

• Debugging is done by the programmer

to fix the errors during the debugging

phase.

Question

• Distinguish between testing and debugging. (2mks)

Answer

• Testing is performed by a tester or end user to find

bugs, faults or error in the program. The tester reports

to the programmer or program development team.

However, Debugging is the process of fixing the errors

found by the testers. Debugging is done by the

programmer to fix the errors during the debugging

phase.

Types of testing

• What type(s) of testing have we been doing so far?

Dry Run Testing

• Dry-running or desk checking or tracing

involves executing the program manually by

using input values for variables and recording

what takes place after each instruction is

executed.

• Tracing is a technique that allows the user to

detect any logic errors in the program or

algorithm.

Trace Tables• A trace table is a table that is completed by

tracing the instruction of the algorithm with

given data to arrive at solutions.

• In designing the table, draw a column for

each variable used in the algorithm and draw

enough rows to form the cells to store the

values.

• There should also be a heading ‘Output’ to

record what is printed.

Trace Tables1. Choose simple input test data which is valid. Two or three sets

of data is valid.

2. Establish what the expected results should be for each teat

case. This is do a manual solution beforehand.

3. Create a trace table of all the variables in the algorithm.

4. Walk the first test case through the algorithm, keeping a step

by step record of the contents of each variable in the table as

the data passes through the logic until the algorithm reaches

its logical end.

5. Check that the expected result established in step two matches

the actual result developed in step 4

6. Repeat the process using a different set of data.

Example

Super six is the name of the junior cricket

team. The coach of super six has hired you to

design a program to provide him with

statistics after each match. Design an

algorithm that reads a list consisting of the

number of runs scored by each batsman in

the team. There are six batsmen in the team.

Compute and print the average number of

runs scored by the team. Solution

Computer Testing

• Computer testing

– involves running the program using

test data to discover any errors in

the program.

Computer Testing

• Computer testing involves the following

steps:

– Compile the program.

– A computer can only execute a program written in

machine language. Before the computer can run

the Pascal program, the latter must be converted to

machine language.

– The source code must be converted into machine

language. The program which does this is a

compiler. The compiler will check for errors in the

program .e.g. syntax errors

Computer Testing

• Run the program.

– The user requests the computer to execute the

program and the user supplies data to the program

for which he or she knows the answer. Such data is

called test data.

– f the program does not give the correct answers the

user knows that the program has at least one logic

error. If the program contains logic errors we must

debug the program; find and correct those errors.

Computer Testing

• The first step in computer testing is translating the

high level program into machine code.

• The program written in the specific programming

language is called the source code. The source code

is translated into object code by the compiler.

Programmers write programs in a form called source

code.

• The source code consists of instructions in a

particular language, like C or FORTRAN. Computers,

however, can only execute instructions written in a

low-level language called machine language.

Computer Testing• To get from source code to machine language, the

programs must be transformed by a compiler.

• The compiler produces an intermediary form called

object code. Object code is often the same as or

similar to a computer's machine language.

• The final step in producing an executable program is to

transform the object code into machine language, if it

is not already in this form.

• This can be done by a number of different types of

programs, called assemblers, linkers, and loaders.

Computer Testing

• Converting a program to machine language is

performed by a translator program.

• These are programs that translate a specific

program from a high level language to

machine language that the computer can

understand. Interpreters, compilers and

assemblers are all translators.

Interpreter

• An interpreter translates the source program line by

line and if an error is detected then translation is

aborted.

• If no errors are detected the interpreter instructs the

control unit to execute the translated instruction.

• This cycle is repeated for each instruction. Therefore

the interpreter translates one instruction at a time

while the program is being executed.

• Translated codes are not saved; therefore each time

the program is executed, translation is necessary.

Interpreter

Advantages

• It translates one instruction at a time; therefore it uses

a minimum amount of memory.

• It is also helpful in the debugging process because the

interpreter can relate error messages to the instruction

being executed

Disadvantage

• Each time the program is executed time is spent

interpreting, hence a slower execution time.

Compiler

• A compiler translates all program instructions at one

time and produces machine language which can be

executed. Error checks are performed and an error

summary is used. This is not done at run time.

• The translated codes are known as object codes and

are saved as a file on a disk. The object code has an

EXE file extension. It is then loaded or linked and

executed.

• The object code is executed each time the program is

run but the source code needs to be compiled only

once.

Compiler

Advantages

• EXE files execute faster than source codes. The object codes

are saved and can be run at any time.

• Object codes are harder for a user to change than source

codes

• The compiler checks the source code for syntax errors during

compilation

Disadvantages

• As the entire program is translated it uses much more of the

computer’s memory.

Assembler

• The assembler translates mnemonic type instruction to

machine code.

• It translates low-level languages to machine language.

• The assembler program takes each program statement

in the source program and generates a corresponding

bit stream or pattern (a series of 0's and 1's).

Run the Program

• The second step in computer testing is to

run the program.

• The user requests the computer to execute

the program.

• The two terms commonly used with program

execution are linking and loading.

Linking

• A compiled object program is not executable by itself.

It needs to be combined with other system modules to

form an executable program.

• A linker also called a link editor and binder is a

program that combines object modules to form an

executable program.

• Linking combines various pieces of code and data

together to form a single executable object than can

be loaded in memory. Linking can be done at compile

time at load time or at run time.

Loading

• Loading involves copying a program from the

hard disk to main memory in order to put the

program in a ready to run state.

Executing The Program

• Program execution is the process whereby the program

is dispatched to the CPU.

• In many of the language compilers today, the process

of compiling, linking and executing are transparent to

the user.

• On some menu- driven systems the user selects

compile from the menu and the program is compiled

and linked from this single option.

• On other systems selecting ‘run’ results in the program

being linked and executed.

Program Execution

When the program is being executed or run the

user supplies test data to discover any errors in

the program. There are three types of errors:

• Syntax errors

• Logic errors

• Run-time errors

Syntax Errors

• Syntax errors are mistakes made by a non

conformance to the grammatical rules of the

programming language.

• For example if we forget to terminate an assignment

statement with a semi- colon or if a reserved word was

used incorrectly.

• Syntax errors stop the source code being converted to

machine code.

• Syntax errors can be easily located and corrected as

the compiler usually issues messages which identify

the location of the errors.

Logic Error• Logic errors occur due to out of sequence instructions,

faulty comparisons and selections.

• For example in order to find the average of three

numbers, the numbers must be entered and added

before dividing by three. Dividing by three before

entering the numbers would be a logic error.

• The program will usually compile.

• Compilation with logic errors does not generate any

syntax errors or warning messages but when the

program is run it produces the wrong results.

Runtime Error

• Run-time errors are errors that occur after the

program has been tested and debugged.

• They occur during the execution and running

of the program.

• They usually occur due to events such as

division by zero or lack of memory for the

computer to manipulate the data.