Testing Components in the Context
of a System
CMSC 737
Fall 2006
Sharath Srinivas
Outline

Introduction to COTS

Advantages of COTS

Challenges in testing Components

Techniques for building testable components

Regression Testing of Component Systems

Conclusions
Introduction

What is Component Based Software Engineering (CBSE)?

This approach is based on the idea to develop software
systems by selecting appropriate off-the-shelf components
and then assemble them with a well-defined software
architecture.

CBSE has three major functions:



Developing software from prefabricated, reusable
parts.
The ability to use those parts in other applications.
Easily maintaining and customizing those parts to
produce new functions and features.
Introduction…

What is a Commercial Off the shelf (COTS) component:




A component is an independent and replaceable part of a system
that fulfills a clear function.
A component works in the context of a well defined architecture.
A component communicates with other components by its
interfaces.
Can be developed by different developers, using different
languages and different platforms.
Component 1
Component
Component 2
Software system
repository
select
Component n
assemble
Advantages of COTS

Development cost is reduced

Development time is reduced

Complex systems can be built by reusing preexisting components

Testing effort is reduced.
Component Based Systems: Architecture

Layman’s interpretation of Component Based
System:
Developer
Builds
Component
Developer
Tests
Component
Final Software
Product
Component Repository
with adequately tested
components
Component User
uses the components
Component Based Systems: A cautionary
Tale-Ariane example

Ariane Flight 501 crashed 30 sec after take-0ff

One of the reasons for the failure of the first Ariane 5 was that a
conversion to integer its software failed (overflow)

This code was taken from Ariane 4, and had been successfully
tested for Ariane 4.

But Ariane 5 had a higher initial velocity and was heavier than
Ariane 4.

The story learnt: Even adequately tested components can fail when
the context in which it is used changes.
Testing Components: Challenges

Testing is done by the developer.

System Requirements not available. Instead the developer
has to use Component specifications.

Unpredictable Environment.

Unpredictable interaction with other components.
Context Sensitive Component Testing:
Challenges

Testing is done by the Component User.

Unavailability of source code.

Source code in various languages.

Dependencies and interactions among components is
complex.
Coverage Notions for Context Sensitive
Component Testing
Component Services are accessible through interfaces.
Coverage Notions for Context Sensitive
Component Testing…


Interface Coverage criterion: Requires that all
interfaces for a component should be exercised at least
once.
Similar to Black box testing.
Test these 2
interfaces
Interface 1
Interface 2
Coverage Notions for Context Sensitive
Component Testing…

Event Coverage Criterion:

Test an interface against all its possible
invocations
Interface 1
Interface 2
Interface 1
Component 1
Interface 2
Component 2
Interface 1
Interface 2
Component 3
Test Interface 1 of component 3
invocated by Interface1 of
Component1.
Test Interface 1 of Component 3
invocated by Interface 2 of
component 2
Coverage Notions for Context Sensitive
Component Testing…

Context Dependency Test Coverage criterion:


Sometimes events can have sequential dependencies on each
other and the order in which they are triggered can result in
different program behavior.
Such dependencies are called context dependencies.
Interface 1
Interface 2
Component 1
Interface 1
Interface 2
Component 2
Interface 1
Component 3
•Test all possible operational sequences in the in the component
•Similar to path Coverage
Interface 2
Coverage Notions for Context Sensitive
Component Testing…

Content Dependency test criterion

A content dependency exists between 2 interfaces I1
and I2 if an operation of I2 modifies the value of a
variable used in an operation of I1.

In this case I2 is said to be content dependent on I1.

Test all the content dependencies in the software.

Similar to All Def-Use criterion
Coverage Notions for Context Sensitive
Component Testing…
Testable COTS components

Techniques for building testable components






Built In tests
Interface Probing
Traceable Components
Self testing components
State Machine Models….
All these techniques involve the efforts of both the
Component developer and Component User
Built In tests

The developer Packages components with the test
cases.

These test cases may be executed on the component by
using a test executor.

Using built in test cases a component user can validate
the behavior of the COTS functionalities.
Interface Probing

Component users might employ this technique to
understand the component functionalities.

The functionality can then be used as the basis for
creating test oracles.

The component developer can reduce the effort
required to determine component properties by
automating certain aspects of interface probing.
Traceable Components

Tractability is a facility that a component provides to
track its internal and external behavior.

Tractability can be used to create test oracles.
Self Testing Components

Augment the component with functionality of analysis
and testing tools.

A component augmented accordingly is capable of
performing some or all activities of the component user’s
testing process.

Component can run in 2 modes:


Normal mode
Maintenance mode
State Machine Models

Techniques discussed in the previous slides are
techniques for better exchange of information between
Component developer and user.

Based on the knowledge gained the component user has
to write test cases to validate if the component will work
in its context.

An automated technique to check if a component will
work in its context is needed
State Machine Model

Test cases generated for testing components in their
context.

This component considers each component as a FSM.

For representing a system and its context all the Finite
State Machines are combined together to form a
Component Based Flow Graph (CBFG)
State Machine Models…
State Machine Model

Based on the CBFG test cases that are context
adequate and content adequate are generated.

Problem in State Machine Models: The testing effort of a
component can be greater than the re-development
effort of the same component!
Modified CBS Architecture
Developer
Builds
Testable
Components
Final Software
Product
Developer
Tests
Components
User tests the
COTS in their
Context
Component Repository
with adequately tested
components
Component
User validates
the components
Regression Testing of Component
Systems

Software built using components have system
components and COTS.

New challenges:
 System components might evolve while COTS
components remain static.
 COTS components might evolve while the system
components remain static.
 Both COTS and system components can evolve.
Conclusions

Testing components in the context of their system is not trivial!

Current research is focusing on 'building testable components'
than 'testing components in their context'

This gives an indication that if a component is not testable it is
difficult/ impossible to test it in it in the context of its system.

Future research in this field might focus on making use of the
‘testable components’ to automate testing components in the
context of their system.
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Testing Component Based Software Architecture