UNIVERSITY OF MALTA
FACULTY OF ICT
Department of Computer Science
B.Sc. (Hons.) ICT – 3rd Year
June 2012 Assessment Session
CPS3222: Fundamentals of Software Testing
19th April 2012
Sample Paper
Answer question one and any other two questions. If more than three questions are answered, only the first three questions in the booklet will be taken
into account. The mark of this exam will contribute towards 50% of the final
mark of CPS3222.
Green Technologies Ltd is a startup company which produces software
for the efficient use of energy and has been in operation for five years. Their
flagship product, GreenHome Pro, uses input feeds from various sensors
around a house and in turn monitors and controls the electricity usage of
individual appliances in the home. For example, if the lights are on in a
particular room but sensors in the room have not sensed movement for more
than five minutes, the lights will be turned off. System behavior is controlled
by a user-configurable usage profile.
1. [Compulsory]
The company is planning to implement a web-based management console for GreenHome Pro and the product manager has provided a list of
languages, operating systems and browsers which must be supported.
These are listed in Table 1 and result in 250 possible language-OSbrowser combinations. Considering that the product requires the execution of approximately 500 test cases, resulting in a total of 125,000
tests, the technical manager has turned to you for help.
a. Given the substantial combinatorial challenge involved with testing
all Browser/OS/Language combinations, discuss different overall
test case design strategies which you would use. What are the
pros and cons of each? [5 marks]
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#
1
2
3
4
5
6
7
8
9
10
Language
English
Spanish
Italian
French
Cantonese
Operating System
Windows XP
Windows Vista
Windows 7
Mac OS X
Linux
Browsers
Internet Explorer 7
Internet Explorer 8
Internet Explorer 9
Internet Explorer 10
Chrome
Firefox 9
Firefox 10
Firefox 11
Safari
Opera
Table 1: The list of supported languages, operating systems and browsers as
required by the product manager.
b. The product manager has stated that he is willing to compromise
for the first release of the product. The product can support (i)
English and Italian languages, (ii) Windows 7 and Mac OS X in
terms of operating systems and finally (iii) Firefox 11 and Chrome
when it comes to browsers. Whilst this results in only 8 possible
combinations, the fact that there are 500 test cases for each combination still leads to a staggering 4000 tests. Your manager wants
to reduce this by half whilst maintaining a sufficient level of coverage. Produce a list of Browser/OS/Language combinations which
you feel will provide adequate coverage. Explain how your choice
of combinatorial test case design technique works and why you
chose it for this particular case. [10 marks]
As a developer on the GreenHome Pro product, you have been asked
to implement and maintain a unit testing suite for the system. You
look into this and find the following class:
public class Controller()
{
public void AutoSetLights(Room room) {
// Gain access to motion sensor
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MovementSensor motionSensor = new MovementSensor(room);
// Gain access to lights
LightController lightController = new CeilingLightController(room);
// Create clock instance
Clock clock = new Clock();
/**
* Lights are only permitted to be on at the following periods:
*
1. Early morning 6:00am - 8:00am
*
2. Late evening 7:00pm - 11:00pm
*
* If there is no recent movement in the room,
* the light will be turned off.
*/
int currentHour = clock.getCurrentHour();
if (room.inhabitant().isChild() && currentHour >= 20) {
//After 8pm, only night lights are used in the children’s rooms
lightController = new NiteLightController();
}
if ( (currentHour >= 6 && currentHour <= 8) ||
(currentHour >= 19 && currentHour <= 23)) {
if (!motionSensor.recentMovement()) {
lightController.switchOff();
}
}
}
}
c. One of the biggest challenges of unit testing is the isolation of the
method under test. Why is this important and why is it difficult?
Explain the concept of test doubles and discuss how the different
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types of test doubles can help alleviate the isolation problem. [15
marks]
d. The code in this sample suffers from testability issues. Write a
testable version of the code given in the sample, explaining what
testability issues you solved and what test pattern you applied to
do so.[15 marks]
e. Describe a number of test cases which you think sufficiently test this
code. E.g. “I would run a test at 2pm and check that the light
is turned of”. What technique(s) did you use to design your test
cases? [5 marks]
2. [Optional]
The software architect has asked you to recommend an integration test
approach for this particular system.
a. Discuss the four main levels of testing, identifying the scope of each
type and who would typically be responsible for it. [5 marks]
b. How would you relate regression testing to unit testing? Mention
three types of errors which are typically found during integration
testing [5 marks].
c. How would you categorise different integration testing strategies?
Discuss and related four different approaches to integration testing
whilst making sure to pick at least one strategy from each category
you provide in the first part of this question. [10 marks]
d. What integration testing strategy would you recommend for this
particular product? Explain the rational behind your choice. [5
marks]
3. [Optional]
Based on market research, the company has determined that their typical users tend to act in certain patterns on a daily basis. Your manager
would like to take advantage of this knowledge and use it in the testing
process by creating a user behaviour model and then using the model to
generate and execute test cases against the system. A user’s behaviour
is composed of a sequence of the following actions:
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(a) Leave home
(b) Enter home
(c) Go to kitchen
(d) Go to bedroom
(e) Turn light on
(f) Turn light off
a. Discuss model-based testing in the context of this scenario and argue
for (or against) its use as you deem fit. [5 marks].
b. Select a type of model to use in this scenario and create a model
that depicts possible user behaviours. Briefly discuss and justify
your approach and the model itself. You may assume that when
someone leaves the house, they are gone long enough for the lights
to have been automatically turned off. [10 marks]
c. Discuss two approaches to model-based test-case generation. What
are the pros and cons of each one and which would you recommend for this particular context? How would you measure the
effectiveness of these approaches? [10 marks]
4. [Optional]
Consider the code fragment for the method AutoSetLights(Room)
from question 1.
a. Constract a control flow graph for this code fragment. [7 marks]
b. Referring to the code fragment, demonstrate how 100% statement
coverage does not necessarily lead to 100% branch coverage. Also,
demonstrate how a fault may still be introduced if you achieve
100% branch coverage. What coverage criteria can be used to
preempt the latter problem and why? [4 marks]
c. Construct a data flow model of the code fragment and identify all
definition-use pairs. Also identify any paths which lead to a definition being killed. [8 marks]
d. How is data flow analysis useful in testing? Define two data-flow
based coverage criteria and identify one possible complication related to data-flow based adequacy criteria in general. [6 marks]
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end of paper