Testing
Testing
Types of Errors
Test Data
Dry running
Program Trace table
What is Testing?

Testing is the process of finding errors
within the software.

Testing can be carried out at all stages of the
system development lifecycle

At each stage a certain test will be carried
out

This makes sure the software is working as
you would like it to
Test Plan

Before you start testing something you will have what
is called a test plan

The plan will describes each item that needs to be
tested

The test plan provides
◦ instructions to be carried out
◦ test data (inputs)
◦ the expected outcomes

The set of test data and expected outcomes form a
test case.
Types of Testing

There are a various number of techniques
that can be applied that help select a test
case that will find the largest number of
errors

The two techniques we will be looking at
are
1. Black Box techniques
2. White Box techniques.
Black Box Technique

Black box techniques see the software
as a ‘black box’ which has inputs and
outputs

No understanding of what is happening
within the black box is needed

When testing, suitable inputs are selected
based upon the running of the system
White Box Techniques

White box techniques analyse the
structure and logic of the program.

This is then used both to help monitor
the detail of testing and to guide the
selecting of appropriate test data
Errors

Errors are a fault or a mistake in a program
that causes the program to produce wrong
results or not to work at all

Most computers attempt to indicate the
source of an error by producing error
messages

There are many different types of errors
that could be found
Syntax Errors

Syntax errors are caused by forgetting certain codes
and statement structures of the programming
language being used

The program will not understand some statements
because they do not obey the programming
language’s rules

The compiler will find these errors

There can be various types of syntax errors, and the
following are some syntax errors examples using
JAVA.
Examples
Code
Syntax Error
System.out.plintln(“Hello”);
prlintln is misspelt.
public static void main (String args[]){
In this case, the syntax error is
class test{
caused by the misplacement of
statements, because class must
}
appear before public static void
}
main…
…
Here, the syntax error is the
if (x>5)
System.out.println(“Bigger”)
omission of the ; at the end of
the println statement.
Logical Errors

A logical error is a mistake found in the
actual design of a program

An example is a branch to a wrong
statement or the use of the wrong
mathematical operation

Logical errors can be found by gaining the
wrong results

The compiler does not notice these errors
Examples
Logical Error
Code
Average=5+10+3/3;
Here,
the
average
will
be
worked out incorrectly because
5+10+3
is
not
enclosed
in
brackets, hence the result will
not be correct but it will be still
worked out.
if (x>5)
System.out.println (“X is smaller than 5“);
In this case, the logical error is
in
the
because
println
it
will
statement
display
the
incorrect message since if x>5
the correct message will be X is
bigger than 5.
Run Time Errors

Run time errors are errors which are shown when the program is
actually running

Examples;

1.
Division by Zero is caused when the program tries to divide something by
0
2.
Lack of Memory, this occurs when the program requires more memory
than there is available hence it will not be able to function properly.
3.
External Errors, such as an error in printing, because no printer could be
found or it is turned off.
4.
Unusual Data, which can occur when the user enters incorrect data. For
example, if the user is asked to input a few numbers to add them up, and
letters are entered, a runtime error will occur, because letters cannot be
added.
Run Time errors can be prevented by writing statements to control
them. For example, if the user needs to enter numbers, and the
user enters letters, the program should be able to identify this and
let the user know
Test Data

When we test our programs we should first create a test
plan where the possible values to be tested are listed down

Then we would go through the test plan to be able to test
different areas of the program.

For example, if the program asks the user to enter his/her
name there would be various test data which we can be use;
1.
2.
3.
4.

Entering the actual name,
Leaving it blank,
Entering numbers instead of letters,
Entering a single letter.
Test Data
All the possible answers will be tested by providing the
inputs above
Dry Running

Dry running a program is basically working through a section
of a program manually.

Dry running a program is useful for finding run-time errors

A dry one is done in parts by taking one section of the
program at a time and not the whole program all at once

A program trace table is produced before the dry run starts,
this table contains;
◦ A column showing the instruction executed
◦ columns for the contents of each variable
Trace table

The programmer uses the instructions from the
trace table, adding a new line to the trace table
each time an instruction is run.

The new line of the trace table shows the
instruction (by its line number, and show any
changes to the variables)
Example
Statement H
W
A
1: Input H
5
2: Input W
5
15
3:A=H*W
5
15
75
4: Print A
5
15
75
5: GoTo 2
5
15
75
Output
Comment
Get Height
Get Width
Calculate Area
75
Print Area
Go back for new pair values. This is the error, this line
should be GoTo 1/
2: Input W
5
20
75
3:A=H*W
5
20
100
Get Width = we haven’t updated the height