Transcript Lecture 1 for Chapter 9, Testing

Using UML, Patterns, and Java
Object-Oriented Software Engineering
Chapter 11: Testing
Outline
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Terminology
Types of errors
Dealing with errors
Quality assurance vs Testing
Component Testing
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System testing
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Function testing
Structure Testing
Performance testing
Acceptance testing
Installation testing
 Unit testing
 Integration testing


Testing Strategy
Design Patterns & Testing
Modified from Bruegge & Dutoit’s originals
Object-Oriented Software Engineering: Using UML, Patterns, and Java
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Terminology
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Reliability: The measure of success with which the observed
behavior of a system confirms to some specification of its
behavior.
Failure: Any deviation of the observed behavior from the
specified behavior.
Erroneous State: The system is in a state such that further
processing by the system will lead to a failure.
Fault (Bug): The mechanical or algorithmic cause of an error.
There are many different types of errors and different ways how
we can deal with them.
Modified from Bruegge & Dutoit’s originals
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Examples of Faults and Errors

Faults in the Interface
specification
 Mismatch between what the
client needs and what the
server offers
 Mismatch between
requirements and
implementation

Algorithmic Faults
 Missing initialization
 Branching errors (too soon,
too late)
 Missing test for nil
Modified from Bruegge & Dutoit’s originals
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Mechanical Faults (very
hard to find)
 Documentation does not
match actual conditions or
operating procedures
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Errors
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Stress or overload errors
Capacity or boundary errors
Timing errors
Throughput or performance
errors
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Dealing with Faults
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Fault avoidance (without execution):
 Use good programming methodology
 Use version control to prevent inconsistent system
 Perform inspections and verification to catch algorithmic bugs

Fault detection (through system execution):
 Testing: Create failures in a planned way
 Debugging: Start with an unplanned failures
 Monitoring: Deliver information about state. Find performance bugs

Fault tolerance (recover from failure once the system is released):
 Data base systems (atomic transactions)
 Modular redundancy
 Recovery blocks
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Testing
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
Testing is NOT the process of demonstrating that faults are not
present.
Testing is the systematic method of detecting faults by creating
failures and erroneous states in a planned way.
 It is impossible to completely test any nontrivial module or any
system
 Testing can only show the presence of bugs, not their absence
(Dijkstra)

Other validation methods:
 Inspections and reviews detect faults by using a structured
approach to reading the code and design artifacts.
 Formal verification detects faults through mathematical proofs of
correctness.
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Testing takes creativity
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Testing often viewed as dirty work.
To develop an effective test, one must have:




Detailed understanding of the system
Knowledge of the testing techniques
Skill to apply these techniques in an effective and efficient manner
Testing is done best by independent testers
 We often develop a certain mental attitude that the program should
in a certain way when in fact it does not.

Programmer often stick to the data set that makes the program
work
 "Don’t mess up my code!"

A program often does not work when tried by somebody else.
 Don't let this be the end-user.
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Testing Activities
Subsystem
Code
Subsystem
Code
Unit
Test
Unit
Test
Tested
Subsystem
Tested
Subsystem
Requirements
Analysis
Document
System
Design
Document
Integration
Test
Integrated
Subsystems
Functional
Test
User
Manual
Functioning
System
Tested Subsystem
Subsystem
Code
Unit
Test
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All tests by developer
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Testing Activities continued
Client’s
Understanding
of Requirements
Global
Requirements
Validated
Functioning
System PerformanceSystem
Test
Accepted
System
Acceptance
Test
User
Environment
Installation
Test
Tests by client
Tests by developer
User’s understanding
Tests (?) by user
Modified from Bruegge & Dutoit’s originals
Usable
System
Object-Oriented Software Engineering: Using UML, Patterns, and Java
System in
Use
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Fault Handling Techniques
Fault Handling
Fault Avoidance
Design
Methodology
Verification
Fault Tolerance
Fault Detection
Atomic
Transactions
Reviews
Modular
Redundancy
Configuration
Management
Debugging
Testing
Unit
Testing
Modified from Bruegge & Dutoit’s originals
Integration
Testing
System
Testing
Correctness
Debugging
Object-Oriented Software Engineering: Using UML, Patterns, and Java
Performance
Debugging
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Quality Assurance encompasses Testing
Quality Assurance
Usability Testing
Scenario
Testing
Fault Avoidance
Verification
Prototype
Testing
Product
Testing
Fault Tolerance
Configuration
Management
Atomic
Transactions
Modular
Redundancy
Fault Detection
Reviews
Walkthrough
Inspection
Unit
Testing
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Debugging
Testing
Integration
Testing
System
Testing
Correctness
Debugging
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Performance
Debugging
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Design and Code Review or Inspection
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A formalized procedure for reading design and code artifacts with the
purpose of detecting faults.
Involves a team of developers in the role of reviewers.
Traditional steps:
 Preparation – reviewers become familiar with the design or code and
record any issues found in the process
 Meeting – a reader paraphrases the design or code and the reviewers raise
issues as the reader proceeds at a measured reading rate; a moderator
controls the pace of the meeting and keeps discussions focused
 Rework – the author resolves the issues and repairs the faults
 Follow-up – the moderator checks the rework and determines the
disposition of the inspection (accept, accept with fixes, re-review)


Inspections are usually done at the unit or component level
Inspections complement unit testing as they tend to find different types of
faults
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Types of Testing

Unit Testing:
 Individual subsystem
 Carried out by developers
 Goal: Confirm that subsystems is correctly coded and carries out
the intended functionality

Integration Testing:
 Groups of subsystems (collection of classes) and eventually the
entire system
 Carried out by developers
 Goal: Test the interface among the subsystem
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System Testing

System Testing:
 The entire system
 Carried out by developers
 Goal: Determine if the system meets the requirements (functional
and global)

Acceptance Testing:
 Evaluates the system delivered by developers
 Carried out by the client. May involve executing typical
transactions on site on a trial basis
 Goal: Demonstrate that the system meets customer requirements
and is ready to use

Implementation (Coding) and testing go hand in hand
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Unit Testing
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Informal:
 Incremental coding
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Static Analysis:
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Hand execution: Reading the source code
Walk-Through (informal presentation to others)
Code Inspection (formal presentation to others)
Automated Tools checking for
 syntactic and semantic errors
 departure from coding standards
Dynamic Analysis:
 Black-box testing (Test the input/output behavior)
 White-box testing (Test the internal logic of the subsystem or object)
 Data-structure based testing (Data types determine test cases)
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Black-box Testing
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Focus: I/O behavior. If for any given input, we can predict the
output, then the module passes the test.
 Almost always impossible to generate all possible inputs ("test
cases")
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Goal: Reduce number of test cases by equivalence partitioning:
 Divide input conditions into equivalence classes
 Choose test cases for each equivalence class. (Example: If an object
is supposed to accept a negative number, testing one negative
number is enough)
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Black-box Testing (Continued)

Selection of equivalence classes (No rules, only guidelines):
 Input is valid across range of values. Select test cases from 3
equivalence classes:



Below the range
Within the range
Above the range
 Input is valid if it is from a discrete set. Select test cases from 2
equivalence classes:



Valid discrete value
Invalid discrete value
Another solution to select only a limited amount of test cases:
 Get knowledge about the inner workings of the unit being tested =>
white-box testing
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White-box Testing
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Focus: Thoroughness (Coverage). Every statement in the
component is executed at least once.
Types of white-box testing
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
Statement Testing
Loop Testing
Path Testing
Branch Testing
State-based Testing
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White-box Testing (Continued)


Statement Testing (Algebraic Testing): Test single statements
(Choice of operators in polynomials, etc)
Loop Testing:
 Cause execution of the loop to be skipped completely. (Exception:
Repeat loops)
 Loop to be executed exactly once
 Loop to be executed more than once

Path testing:
 Make sure all paths in the program are executed

Branch Testing (Conditional Testing): Make sure that each
possible outcome from a condition is tested at least once
if ( i = TRUE) printf("YES\n");else printf("NO\n");
Test cases: 1) i = TRUE; 2) i = FALSE
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White-box Testing Example
FindMean(float Mean, FILE ScoreFile)
{ SumOfScores = 0.0; NumberOfScores = 0; Mean = 0;
Read(ScoreFile, Score); /*Read in and sum the scores*/
while (! EOF(ScoreFile) {
if ( Score > 0.0 ) {
SumOfScores = SumOfScores + Score;
NumberOfScores++;
}
Read(ScoreFile, Score);
}
/* Compute the mean and print the result */
if (NumberOfScores > 0 ) {
Mean = SumOfScores/NumberOfScores;
printf("The mean score is %f \n", Mean);
} else
printf("No scores found in file\n");
}
Modified from Bruegge & Dutoit’s originals
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White-box Testing Example: Determining the Paths
FindMean (FILE ScoreFile)
{ float SumOfScores = 0.0;
int NumberOfScores = 0;
1
float Mean=0.0; float Score;
Read(ScoreFile, Score);
2 while (! EOF(ScoreFile) {
3 if (Score > 0.0 ) {
SumOfScores = SumOfScores + Score;
NumberOfScores++;
}
5
Read(ScoreFile, Score);
4
6
}
/* Compute the mean and print the result */
7 if (NumberOfScores > 0) {
Mean = SumOfScores / NumberOfScores;
printf(“ The mean score is %f\n”, Mean);
} else
printf (“No scores found in file\n”);
9
}
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Constructing the Logic Flow Diagram
Start
1
F
2
T
3
T
F
5
4
6
7
T
F
9
8
Exit
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Finding the Test Cases
Start
1
a (Covered by any data)
2
b (Data set must contain at least one value)
(Positive score) d
c
4
(Data set must
f
be empty)
6
7
(Total score < 0.0) i
8
e (Negative score)
5
h (Reached if either f or
g
e is reached)
j (Total score > 0.0)
9
k
Modified from Bruegge & Dutoit’s originals
3
Exit
l
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Test Cases



Test case 1 : ? (To execute loop exactly once)
Test case 2 : ? (To skip loop body)
Test case 3: ?,? (to execute loop more than once)
These 3 test cases cover all control flow paths
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Dealing with Polymorphism

Polymorphism enables invocations to be bound to different
methods based on the class of the target
 Leads to compact code and increased reuse
 Introduces many new cases to test

Strategy
 Consider all possible dynamic bindings and convert the invocation
into an if-then-else statement for each potential dynamic binding
 Perform path testing
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State-Based Testing



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Instead of comparing actual and expected outputs, state-based
testing compares resulting state with expected state
Each test case consists of starting state, stimuli, expected next
state
Useful for classes with complex state transition diagrams
Steps
 Derive test cases from the statechart model
 For each state, derive equivalence classes of stimuli to activate each
transition
 Instrument each attribute of the class in order to compute the new
state of the class
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Example Statechart Diagram
3.pressButtonsLAndR
2.
pressButtonL
pressButtonR
1.
MeasureTime
SetTime
6.
pressButtonL
pressButtonR
4.after 2 min.
5.pressButtonsLAndR/beep
7.after 20 years
8.after 20 years
DeadBattery
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Comparison of White & Black-box Testing

White-box Testing:

 Potentially infinite number of
paths have to be tested
 White-box testing often tests
what is done, instead of what
should be done
 Cannot detect missing use cases

Black-box Testing:
 Potential combinatorical
explosion of test cases (valid &
invalid data)
 Often not clear whether the
selected test cases uncover a
particular error
 Does not discover extraneous
use cases ("features")
Modified from Bruegge & Dutoit’s originals


Both types of testing are needed
White-box testing and black box
testing are the extreme ends of a
testing continuum.
Any choice of test case lies in
between and depends on the
following:




Number of possible logical paths
Nature of input data
Amount of computation
Complexity of algorithms and
data structures
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The 4 Testing Steps
1. Select what has to be
measured
3. Develop test cases
 Analysis: Completeness of
requirements
 Design: tested for cohesion
 Implementation: Code tests
2. Decide how the testing is
done




Code inspection
Proofs (Design by Contract)
Black-box, white box,
Select integration testing
strategy (big bang, bottom
up, top down, sandwich)
Modified from Bruegge & Dutoit’s originals
 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
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Guidance for Test Case Selection

Use analysis knowledge
about functional
requirements (black-box
testing):
 Use cases
 Expected input data
 Invalid input data


Use implementation
knowledge about algorithms:
 Examples:
 Force division by zero
 Use sequence of test cases for
interrupt handler
Use design knowledge about
system structure, algorithms,
data structures (white-box
testing):
 Control structures

Test branches, loops, ...
 Data structures

Test records fields, arrays,
...
Modified from Bruegge & Dutoit’s originals
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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!
Modified from Bruegge & Dutoit’s originals
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
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Integration Testing Strategy
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

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
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Using the Bridge Pattern to enable early Integration
Testing


Use the bridge pattern to provide multiple implementations
under the same interface.
Interface to a component that is incomplete, not yet known or
unavailable during testing
VIP
Seat Interface
(in Vehicle Subsystem)
Stub Code
Modified from Bruegge & Dutoit’s originals
Seat Implementation
Simulated
Seat (SA/RT)
Object-Oriented Software Engineering: Using UML, Patterns, and Java
Real Seat
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Example: Three Layer Call Hierarchy
A
C
B
E
Modified from Bruegge & Dutoit’s originals
Layer I
F
D
Layer II
G
Layer III
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Integration Testing: Big-Bang Approach
Unit Test
A
Don’t try this!
Unit Test
B
Unit Test
C
System Test
Unit Test
D
Unit Test
E
Unit Test
F
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Bottom-up Testing Strategy




The subsystem in the lowest layer of the call hierarchy are
tested individually
Then the next subsystems are tested that call the previously
tested subsystems
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 subsystem and passes a test case to it
Modified from Bruegge & Dutoit’s originals
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Bottom-up Integration
A
C
B
Test E
E
Layer I
F
D
G
Layer II
Layer III
Test B, E, F
Test F
Test C
Test
A, B, C, D,
E, F, G
Test D,G
Test G
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Pros and Cons of bottom up integration testing


Tests some important subsystems (user interface) last
Useful for integrating the following systems
 Object-oriented systems
 real-time systems
 systems with strict performance requirements
Modified from Bruegge & Dutoit’s originals
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Top-down Testing Strategy




Test the top layer or the controlling subsystem first
Then combine all the subsystems that are called by the tested
subsystems and test the resulting collection of subsystems
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.
SeatDriver
(simulates VIP)
Seat Interface
(in Vehicle Subsystem)
Simulated
Seat (SA/RT)
Object-Oriented Software Engineering: Using UML, Patterns, and Java
Stub Code
Modified from Bruegge & Dutoit’s originals
Seat Implementation
Real Seat
39
Top-down Integration Testing
A
C
B
E
Test A
Test A, B, C, D
Layer I
D
G
F
Layer II
Layer III
Test
A, B, C, D,
E, F, G
Layer I
Layer I + II
All Layers
Modified from Bruegge & Dutoit’s originals
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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.
Possibly a very large number of stubs may be required,
especially if the lowest level of the system contains many
methods.
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
Modified from Bruegge & Dutoit’s originals
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Sandwich Testing Strategy



Combines top-down strategy with bottom-up strategy
The system is view as having three layers
 A target layer in the middle
 A layer above the target
 A layer below the target
 Write drivers and stubs for target layer
 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
Modified from Bruegge & Dutoit’s originals
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Sandwich Testing Strategy
A
C
B
E
Test E
Bottom
Layer
Tests
Layer I
F
D
G
Layer II
Layer III
Test B, E, F
Test F
Test D,G
Test
A, B, C, D,
E, F, G
Test G
Test A,B,C, D
Top
Layer
Tests
Test A
Modified from Bruegge & Dutoit’s originals
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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
Solution: Modified sandwich testing strategy
Modified from Bruegge & Dutoit’s originals
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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 from Bruegge & Dutoit’s originals
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Modified Sandwich Testing Strategy
Double
Test I
A
Test B
C
B
Test E
Triple
Test I
Triple
Test I
Test B, E, F
E
F
D
G
Layer II
Layer III
Double
Test II
Test F
Double
Test II
Layer I
Test D
Test D,G
Test
A, B, C, D,
E, F, G
Test G
Test A,C
Test A
Test C
Double
Test I
Modified from Bruegge & Dutoit’s originals
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Scheduling Sandwich Tests: Example of a
Dependency Chart
Unit Tests
Modified from Bruegge & Dutoit’s originals
Double Tests
Triple Tests
Object-Oriented Software Engineering: Using UML, Patterns, and Java
SystemTests
47
Steps in Integration-Testing
1. Based on the integration strategy,
select a component to be tested.
Unit test all the classes in the
component.
2.. Put selected component together;
do any preliminary fix-up
necessary to make the integration
test operational (drivers, stubs)
3. Do functional testing: Define test
cases that exercise all uses cases
with the selected component
Modified from Bruegge & Dutoit’s originals
4. Do structural testing: Define test
cases that exercise the selected
component
5. Execute performance tests
6. Keep records of the test cases and
testing activities.
7. Repeat steps 1 to 7 until the full
system is tested.
The primary goal of integration
testing is to identify errors in the
(current) component configuration.
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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
 ...
Modified from Bruegge & Dutoit’s originals
 ...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
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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:
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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.
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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 user-oriented test cases have
.
to be developed as well.
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Performance Testing

Stress Testing

 Stress limits of system (maximum # of
users, peak demands, extended
operation)





Compatibility test
 Try to violate security requirements
Modified from Bruegge & Dutoit’s originals
Recovery testing
 Tests system’s response to
presence of errors or loss of
data.

Security testing
Quality testing
 Test reliability, maintain- ability
& availability of the system
 Test backward compatibility with
existing systems

Environmental test
 Test tolerances for heat,
humidity, motion, portability
Configuration testing
 Test the various software and
hardware configurations

 Evaluate response times and
time to perform a function
Volume testing
 Test what happens if large amounts of
data are handled
Timing testing
Human factors testing
 Tests user interface with user
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Test Cases for Performance Testing



Push the (integrated) system to its limits.
Goal: Try to break the subsystem
Test how the system behaves when overloaded.
 Can bottlenecks be identified? (First candidates for redesign in the
next iteration

Try unusual orders of execution
 Call a receive() before send()

Check the system’s response to large volumes of data
 If the system is supposed to handle 1000 items, try it with 1001
items.

What is the amount of time spent in different use cases?
 Are typical cases executed in a timely fashion?
Modified from Bruegge & Dutoit’s originals
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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:
Modified from Bruegge & Dutoit’s originals

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 environment
 Potential customer might get
discouraged
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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
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Test Team
Professional
Tester
Programmer
too familiar
with code
Analyst
User
Test
Team
System
Designer
Configuration
Management
Specialist
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Test Plan










Introduction
Relationship to other documents
System overview (overview of components, esp. for unit test)
Test coverage (features to be tested/not to be tested)
Pass/Fail criteria
Approach
Suspension and resumption
Testing materials (hardware/software requirements)
Test cases
Testing schedule
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Test Case Specification







Test case specification identifier
Test items
Input specifications
Output specifications
Environmental needs
Special procedural requirements
Intercase dependencies
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Test Automation






Regression testing – re-running system and integration tests to
verify that changes to the system do not lead to new failures
and erroneous states.
In practice, many tests need to be repeatedly run as part of
regression testing.
Test automation can save a significant amount of testing effort
and staff needs.
Test cases – specified in terms of sequence of inputs and their
expected outputs
Test harness – automatically executes the test cases and
compares actual output with expected output
This requires an investment to develop.
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Automated Test Infrastructure Example: JUnit
Test
TestResult
run(TestResult)
TestCase
testName:String
run(TestResult)
setUp()
tearDown()
runTest()
TestSuite
run(TestResult)
addTest()
ConcreteTestCase
setUp()
tearDown()
runTest()
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Using JUnit





Write new test case by subclassing from TestCase
Implement setUp() and tearDown() methods to initialize and
clean up
Implement runTest() method to run the test harness and
compare actual with expected values
Test results are recorded in TestResult
A collection of tests can be stored in TestSuite.
Modified from Bruegge & Dutoit’s originals
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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 integration testing
Testing has its own lifecycle


Modified from Bruegge & Dutoit’s originals
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