Types of tests and various steps to take

Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 1
Review: What are the 3 types of quality control
techniques?
 Error prevention
 Error detection
 Testing, debugging
 Error recovery
 Fault tolerance

The 4 Testing Steps
1. Select what has to be
measured
 Completeness of
requirements
 Code tested for reliability
 Design tested for cohesion
2. Decide how the testing is
done
 Code inspection
 Proofs
 Black-box, white box,
 Select integration testing
strategy (big bang, bottom
up, top down, sandwich)
3. Develop test cases
 A test case is a set of test
data or situations that will
be used to exercise the unit
(code, module, system) being
tested or about the attribute
being measured
4. Create the test oracle
 An oracle contains of the
predicted results for a set of
test cases
 The test oracle has to be
written down before the
actual testing takes place

Guidance for Test Case Selection
 Use analysis knowledge
about functional
requirements (black-box):
 Use cases
 Expected input data
 Invalid input data
 Use design knowledge about
system structure, algorithms,
data structures (white-box):
 Control structures
 Test branches, loops, ...
 Data structures
 Test records fields,
arrays, ...
 Use implementation
knowledge about algorithms:
 Force division by zero
 Use sequence of test cases for
interrupt handler

Unit-testing Heuristics
1. Create unit tests as soon as object
design is completed:
 Black-box test: Test the use
cases & functional model
 White-box test: Test the
dynamic model
 Data-structure test: Test the
object model
2. Develop the test cases
 Goal: Find the minimal
number of test cases to cover
as many paths as possible
3. Cross-check the test cases to
eliminate duplicates
 Don't waste your time!
4. Desk check your source code
 Reduces testing time
5. Create a test harness
 Test drivers and test stubs are
needed for integration testing
6. Describe the test oracle
 Often the result of the first
successfully executed test
7. Execute the test cases
 Don’t forget regression testing
 Re-execute test cases every time a
change is made.
8. Compare the results of the test with the
test oracle
 Automate as much as possible

Component-Based Testing Strategy
 The entire system is viewed as a collection of subsystems (sets
of classes) determined during the system and object design.
 The order in which the subsystems are selected for testing and
integration determines the testing strategy
Big bang integration (Nonincremental)
Bottom up integration
Top down integration
Sandwich testing
Variations of the above
 For the selection use the system decomposition from the
System Design

Example: Three Layer Call Hierarchy
A
B C D
G
F
E
Layer I
Layer II
Layer III

Integration Testing: Big-Bang Approach
Unit Test
Database
Unit Test
Network
Unit Test
Event Service
Unit Test
Learning
Unit Test
Billing
Unit Test
UI
System Test
PAID
Don’t try this!

Bottom-up Testing Strategy
 The subsystems in the lowest layer of the call hierarchy are
tested individually
 Then the next subsystems are tested that call the previously
tested subsystems
 Combine the pieces layer-by-layer, from bottom layer on up.
 This is done repeatedly until all subsystems are included in the
testing
 Special program needed to do the testing, Test Driver:
 A routine that calls a particular subsystem and passes a test case to
it

Bottom-up Integration A
B C D
G
F
E
Layer I
Layer II
Layer III
Test D,G
Test F
Test E
Test G
Test C Test
A, B, C, D,
E, F, G
Test B, E, F

Pros and Cons of bottom up integration testing
 Bad for functionally decomposed systems:
Tests the most important subsystem last (e.g. user
interface)
 Useful for integrating the following systems
Object-oriented systems
real-time systems
systems with strict performance requirements

Top-down Testing Strategy
 Test the top layer or the controlling subsystem first
 Then combine all the subsystems that are called by the
previously tested subsystem(s) and test the new collection
 Do this until all subsystems are incorporated into the test
 Special program is needed to do the testing, Test stub :
 A program or a method that simulates the activity of a missing
subsystem by answering to the calling sequence of the calling
subsystem and returning back fake data.

Top-down Integration Testing
A
B C D
G
F
E
Layer I
Layer II
Layer III
Test A
Test
A, B, C, D,
E, F, G
Test A, B, C, D
Layer I
Layer I + II
All Layers

Pros and Cons of top-down integration testing
 Test cases can be defined in terms of the functionality of the
system (functional requirements)
 Writing stubs can be difficult:
 Stubs must allow all possible conditions to be tested.
 A large number of stubs may be required.
 One solution to avoid too many stubs: Modified top-down
testing strategy
 Test each layer of the system decomposition individually before
merging the layers
 Disadvantage of modified top-down testing: Both stubs and drivers
are needed

Sandwich Testing Strategy
 Combines top-down strategy with bottom-up strategy
 The system is viewed as having three layers
A target layer in the middle
A layer above the target
A layer below the target
Testing converges at the target layer
 How do you select the target layer if there are more than 3
layers?
Heuristic: Try to minimize the number of stubs and
drivers

Sandwich Testing Strategy A
B C D
G
F
E
Layer I
Layer II
Layer III
Test D,G
Test F
Test E
Test G
Test A
Test
A, B, C, D,
E, F, G
Test B, E, F
Bottom
Layer
Tests
Top
Layer
Tests

Pros and Cons of Sandwich Testing
 Top and Bottom Layer Tests can be done in parallel
 Does not test the individual subsystems thoroughly before
integration
 Alternative: Modified sandwich testing strategy

Modified Sandwich Testing Strategy
 Test in parallel:
Middle layer with drivers and stubs
Top layer with stubs
Bottom layer with drivers
 Test in parallel:
Top layer accessing middle layer (top layer replaces
drivers)
Bottom accessed by middle layer (bottom layer replaces
stubs)

Modified Sandwich Testing Strategy
A
B C D
G
F
E
Layer I
Layer II
Layer III
Test D,G
Test F
Test E
Test G
Test A
Test
A, B, C, D,
E, F, G
Test B, E, F
Test B
Test D
Test C
Triple
Test I
Double
Test I
Double
Test II
Triple
Test I
Double
Test I
Double
Test II

Which Integration Strategy should you use?
 Factors to consider
 Amount of test harness
(stubs &drivers)
 Location of critical parts in
the system
 Availability of hardware
 Availability of components
 Scheduling concerns
 Bottom up approach
 good for object oriented
design methodologies
 Test driver interfaces must
match component interfaces
 ...
 ...Top-level components are
usually important and
cannot be neglected up to the
end of testing
 Detection of design errors
postponed until end of
testing
 Top down approach
 Test cases can be defined in
terms of functions examined
 Need to maintain correctness
of test stubs
 Writing stubs can be difficult

System Testing
 Functional Testing
 Structure Testing
 Performance Testing
 Acceptance Testing
 Installation Testing
Impact of requirements on system testing:
 The more explicit the requirements, the easier they are to test.
 Quality of use cases determines the ease of functional testing
 Quality of subsystem decomposition determines the ease of structure
testing
 Quality of nonfunctional requirements and constraints determines
the ease of performance tests:

Structure Testing
 Essentially the same as white box testing.
 Goal: Cover all paths in the system design
 Exercise all input and output parameters of each component.
 Exercise all components and all calls (each component is called at
least once and every component is called by all possible callers.)
 Use conditional and iteration testing as in unit testing.

Functional Testing
.
.
Essentially the same as black box testing
 Goal: Test functionality of system
 Test cases are designed from the requirements analysis
document (better: user manual) and centered around
requirements and key functions (use cases)
 The system is treated as black box.
 Unit test cases can be reused, but new test cases oriented to the
end user have to be developed as well.

Performance Testing
 Stress Testing
 Stress limits of system (maximum # of
users, peak demands, extended
operation)
 Volume testing
 Test what happens if large amounts of
data are handled
 Configuration testing
 Test the various software and
hardware configurations
 Compatibility test
 Test backward compatibility with
existing systems
 Security testing
 Try to violate security requirements
 Timing testing
 Evaluate response times and
time to perform a function
 Environmental test
 Test tolerances for heat,
humidity, motion, portability
 Quality testing
 Test reliability, maintain-ability
& availability of the system
 Recovery testing
 Tests system’s response to
presence of errors or loss of
data.
 Human factors testing
 Tests user interface with user

Acceptance Testing
 Goal: Demonstrate system is
ready for operational use
 Choice of tests is made by
client/sponsor
 Many tests can be taken
from integration testing
 Acceptance test is performed
by the client, not by the
developer.
 Majority of all bugs in software is
typically found by the client after
the system is in use, not by the
developers or testers. Therefore
two kinds of additional tests:
 Alpha test:
 Sponsor uses the software at
the developer’s site.
 Software used in a controlled
setting, with the developer
always ready to fix bugs.
 Beta test:
 Conducted at sponsor’s site
(developer is not present)
 Software gets a realistic
workout in target environ-
ment
 Potential customer might get
discouraged

Testing has its own Life Cycle
Establish the test objectives
Design the test cases
Write the test cases
Test the test cases
Execute the tests
Evaluate the test results
Change the system
Do regression testing

Summary
 Testing is still a black art, but many rules and heuristics are
available
 Testing consists of component-testing (unit testing, integration
testing) and system testing
 Design Patterns can be used for component-based testing
 Testing has its own lifecycle

Types of tests and various steps to take

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