1. CS 8532: Advanced Software Engineering
Chapter 13
CS 8532: Advanced Software Engineering
Dr. Hisham Haddad
Class
will
start
momentarily.
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2. Software Testing Strategies
Discussion of Software Testing and
Testing Strategies
Chapter 13

3. Testing Testing is the process of exercising a
program with the intent of finding
errors prior to delivery to the end user, and it requires a strategy.

4. What Testing Shows errors requirements conformance Performance issue
an indication
of quality

5. Who Tests the Software? developer independent tester
Understands the system.
But, will test “gently”
and, is driven by “delivery”
Must learn about the system. B
but, will attempt to “break” it
and, is driven by “quality”

6. The Big Picture Testing is an element of the V&V process.
Verification: The software implements the functional specifications.
Validation: The software is traceable to customer requirements (functional, behavioural, performance). (mapping software components to requirements)
V&V activities = SQA (see chapter 26 on Quality Management)
The testing group works with the developers and reports to the SQA team.
“You can’t test in quality. If it‘s not there before you begin testing, it won’t be there when you finished testing”

7. Testing Strategy (1)
A testing strategy is a plan (road map) that outlines the detailed testing activities (steps, test case design, test execution, effort, time, resources). It results in a Test Specification document.
Many testing strategies are proposed. However, common characteristics of a testing strategies include:
- Testing starts with effective FTR
- Testing starts at the component level and work outward
- Testing is conducted by developers (small projects) and testing groups (large projects)
- Different techniques are relevant at different points in the development process
- Debugging is an activity of any testing strategy

8. Testing Strategy (2) Note 1:
For conventional software, the module (component) is the initial focus, then integration of modules follows.
Note 2:
For OO software, when “testing in the small”, the focus changes from an individual module (the conventional view) to an OO class (or package of classes) that encompasses attributes and operations and implies communication and collaboration.

9. Strategic Issues How do we develop a successful testing strategy?
State software requirements in quantifiable manner to test for quality characteristics
State testing objectives explicitly
Understand the users of the software and develop a profile for each user category (use-cases)
Develop a testing plan that emphasizes “rapid cycle testing”
Build “robust” software that tests itself – exception handling
Use effective FTRs to filter errors prior to testing
Apply FTRs to the test strategy and test cases themselves
Develop a continuous improvement approach for the testing process (collect data and develops metrics)
See page 361

10. Testing Strategy Elements (1)
unit test
integration
test
validation
system

11. Testing Strategy Elements (2)
Unit Testing: testing functionality of individual modules
(using white-box methods).
Integration Testing: testing functionality of integrated modules (using both white-box and black-box methods).
Validation Testing: testing the software for all established requirements (functional, behaviour, performance, reliability, …)
(using black-box methods).
System Testing: testing the software for compatibility with other system elements (HW, users, databases, other systems).
Q: When does testing stop?

12. Unit Testing – Conventional Software
module
to be
tested
test cases
results
software
engineer

13. Unit Testing Environment
Tested
Module
stub
Test driver
RESULTS
interface
local data structures
boundary conditions
independent paths
error handling paths
test cases

14. Unit Testing Errors Some common computational errors:
- Incorrect arithmetic precedence
- Incorrect logical operators or precedence
- Incorrect initialization
- Incorrect symbolic representation of an expression
- Incorrect data type comparisons (different data types)
- Incorrect comparison of variables
- Improper or nonexistent loop termination
- Improper modified loop variables
- Improper boundary checks
- Precision inaccuracy
- Others… (see page 363)

15. Integration Testing Testing Options:
- Non-incremental approach (all at once!)
- Incremental construction strategy (one addition at a time)
Incremental approach:
- Top-Down Integration: start with main and work downward integrating subunits (either depth-first or breadth-first order)
- Bottom-Up Integration: start with atomic unit (working modules) and work upward integrating other units (clusters).

16. Top-down Integration Testing
top module is tested with stubs.
stubs are replaced one at a time,
“depth-first”.
as new modules are integrated some subset of tests is re-run. A B C D E F G
Problem: testing upper-level unit may depend on
a lower-level unit!
Sandwich (Combo) testing may be performed!

17. Bottom-up Integration Testing
drivers are replaced one at a time,
"depth first"
lower modules are grouped into builds and are integrated A B C D E F G
Cluster (build)
Bottom-up integration eliminates the
need for complex stubs!

18. Sandwich Integration Testing
Lower modules that unit B depends on are
grouped into builds that are tested and integrated
Top modules are tested
with stubs A B C D E F G
cluster

19. Integration Testing - Comments
- Possible difficulties writing stubs for top-down testing
- Top-down testing allows testing control module
- The entire program is not tested until the last module is added
- Bottom-up testing seems easier to conduct (no stubs)
- Sandwich testing is a compromise when selecting an integration testing strategy
- Critical modules should be identified and tested as early as possible
- “Test specifications” is a document that contains test plans, procedures, test cases, environment, resources etc…
It becomes part of Software Configuration.

20. Other Integration Testing
Regression Testing: Used to test side affect each time a new module is added.
It is re-execution of subsets of test cases that already been conducted so that side effects (if any) are uncovered.
Smoke Testing: A top-down or bottom-up integration test for “shrink wrapped” software applications that consist of “daily builds” (releases).
Steps:
- Integrate new code into a “build.” ( data files, libraries, reusable modules, and components required to implement functions)
- Design a series of tests to expose errors in the new build. (errors with highest possibility to affect project progress)
- Integrate current build with other builds and smoke test (daily) the entire product.

21. OO Testing
- OO Testing begins by evaluating the correctness and consistency of the OOA and OOD models.
(An approach to Testing the CRC model, next slide)
- The nature of OO software changes testing strategies.
- the concept of the ‘unit’ broadens due to encapsulation
- cannot test class methods in isolation due to object
collaborations and inheritance
- class testing is driven by its methods and behavior (states)
- The notion of Unit testing is replaced by Class testing
- Conventional integration testing (top-down and bottom-up) are not applicable to OO software. Replaced by Class Integration testing

22. Testing the CRC Model
1. Revisit the CRC model and the object-relationship model.
2. Inspect the description of each CRC index card to determine if a delegated responsibility is part of the collaborator’s definition.
3. Invert the connection to ensure that each collaborator that is asked for service is receiving requests from a reasonable source.
4. Using the inverted connections examined in step 3, determine whether other classes might be required or whether responsibilities are properly grouped among the classes.
5. Determine whether widely requested responsibilities might be combined into a single responsibility.
6. Steps 1 to 5 are applied iteratively to each class and through each evolution of the OOA model.

23. OO Testing Strategy Class testing is the equivalent of unit testing
- operations within the class are tested
- the state behavior of the class is examined
Integration testing applies three different strategies:
- thread-based testing: integrates the set of classes required to respond to one input or event
- use-based testing: integrates the set of classes required to respond to one use-case (usage scenario)
- collaboration (cluster) testing: integrates sets of classes required to demonstrate one collaboration (determined from the object relationship and CRC models)

24. Validation Testing
Validation test focus on software conformance with software requirements, and is based on the Validation Criteria, a section of the SRS document.
behavioral characteristics, software configuration items, performance characteristics, documentation, error recovery, maintainability, and others…
Mainly black-box based testing.
Alpha test - acceptance test performed by the customer at the developer’s site to validate system requirements.
Beta test - acceptance test performed by the customer at the customer's site to validate system requirements.

25. System Testing
A series of tests for system compatibility with HW, users, databases, and other systems.
Example tests:
Recovery testing: test the system’s ability to recover from a failure. Force the system to fails and see how it responds.
Security testing: test built-in security methods. Try to gain access as an unauthorized user of the system.
Stress testing: test the system for abnormal conditions (resource allocation). Try to overwhelm the system.
Performance testing: test the system’s run-time performance. Try to cause system degradation and failure.

26. Testing vs. Debugging
Testing uncovers errors; while debugging removes them.
Testing is a process; while debugging is an art.
Debugging outcome is either “error cause is found” or “error cause is not found!”
Debugging is difficult!

27. The Debugging Process test cases new test cases results regression
suspected
causes
identified
corrections
regression
tests
new test
cases

28. Why Debugging is Difficult?
cause may be due to a combination of non-errors (rounding)
cause may be due to a system or compiler error
cause may be due to assumptions that everyone believes
causes may be distributed among processes/tasks
symptom may be irregular due to both HW and SW
symptom may disappear when another problem is fixed
symptom and cause may be geographically separated

29. Debugging Effort to correct the error and conduct regression tests
time required
to diagnose the symptom and determine the cause
to correct the error and conduct regression tests

30. Consequences of Debugging
damage
mild
annoying
disturbing
serious
extreme
catastrophic
infectious
Bug Type
Bug Categories: function-related bugs, system-related bugs, data bugs, coding bugs, design bugs, documentation bugs, standards violations, etc…

31. Debugging Techniques
Brut Force debugging: “let the system find the error!” (memory dumps, run-time traces, and inserted output statements)
Backtracking: trace the code (manually) back to the source of the error.
Cause Elimination:
by induction - make “cause induction hypothesis” and
use test data to prove or disapprove the hypothesis. Or
by deduction - list all possible cause and test them for
elimination.

32. Debugging – Final Thoughts
Don't run off half-cocked, think about the symptom you're seeing.
Use tools (e.g., dynamic debugger) to gain more insight.
If at an impasse, get help from someone else.
Be absolutely sure to conduct regression tests when you do "fix" the bug.

33. Suggested Problems
Consider working the following problems from chapter 13, page 385:
1, 2, 3, 4, 7, and 8.
No submission is required for practice assignments. Work it for yourself!