testing: general requirements, dft, multilevel testing
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Testing: General Requirements, DFT, Multilevel Testing. Testing: General Requirements DFT Multilevel Testing-- System, Black Box, White or Glass Box Tests. Testing--General Requirements and Strategies. Testing--general requirements: thorough ongoing - PowerPoint PPT PresentationTRANSCRIPT
Testing: General Requirements, DFT, Multilevel Testing
Testing:
General Requirements
DFT
Multilevel Testing--
System, Black Box, White or Glass Box Tests
Testing--General Requirements and Strategies
Testing--general requirements:
•thorough
•ongoing
•DEVELOPED WITH DESIGN (DFT--design for test) note: this implies that several LEVELS of testing will be carried out efficiently
Testing: general strategies:
•Fault avoidance: reduce possibility of faults through techniques such as configuration management, good development process
•Fault detection: use debugging and testing to find and remove faults
•Fault tolerance: use techniques such as redundant modules, let them “vote” on what the output should be
Efficiency / How Thoroughly Can We Test?
Testing is difficult:
example: VLSI chip--200 inputs;
2000 flipflops (one-bit memory cells) # exhaustive tests?
What is the overall time to test if we can do1 test / msec? 1 test / msec? 1 test /nsec?
Testing functionality (as with the above chip) is an example of an NP-complete problem, i.e., a problem for which the only algorithms we know to actually find the answer would take time exponential in the problem sizeTesting software is even harder, there are usually semantic issues which are difficult to deal with
“gates”—n2I/O—4n
Good, Bad, and Successful Tests
“Psychology of testing”:
• good test: has a high probability of finding an error
• ("bad test": not likely to find anything new)
• successful test: finds a new error
Most Effective Testing Is Independent
most effective testing: by an "independent” third party
It is more difficult to “see” the errors you have included in your own work:
--subconsciously you want the system to work
--you may know what you intended and overlook what is
actually there
--an independent tester brings a fresh viewpoint to the
question of what works and what doesn’t
--testing requires expertise; common practice of putting the most inexperienced team members in charge of
testing is not really effective
Question: what does this imply about your team testing strategy for the quarter project?
Automated Testing
Automated testing
Testing must be thorough and must be repeated frequently during development.
Thus it is a good candidate for automation.
Example system for automated testing in Java:JUnit (Fig. 11-29)
TestCase
ConcreteTestCase
TestResultTest
run (TestResult)
TestSuite
Testing—UML extension
Example: U2TP—UML 2 Testing Profile (2005 extension to UML)
Extends UML to allow the modeling of testing
Can be used with manual or automated testing
Example: Figure 11-31:
----Context: organize test cases, test components, system under test (SUT)
----Components: set up tests
----SUT: what is being tested
Matching Testing with Design and Language
How will testing match with design/language?
e.g.:
*procedural: example--sort an array—program has access to all array information
*oo: example--develop an "array class”—only the owner class and friends have direct access to the array structure
what kinds of test need to be done in each case?
Testing strategies
At different points in the development cycle, tests may have different goals, e.g.:
--verification--functions correctly implemented (according to specifications) --validation--we are implementing the correct functions (according to requirements)
Design for Testability (DFT)
Design for Testability (DFT)--what makes software "testable"?
• understandability: you understand module, inputs, and outputs
• decomposability: you can decompose into smaller problems and test each separately
• operability: only a few errors possible--incremental test strategy
• controllability: you can control state + input to test
• observability: you can see the results of the test
• simplicity: you choose the “simplest solution that will work”
• stability: same test will give same results each time
Design for Testability (DFT): useful strategies
Some useful strategies:
--pretest: test before carrying out an action example: test divisor is not zero before division
--posttest: test that you got a valid result example: if you are calculating a grade, test that the result is between 0 and 100
--invariant: test that iterations don’t change value/range example: test that loop counter stays within bounds
Spiral design/testing strategy
A general design/testing strategy can be described as a "spiral”:requirements design codesystem test module,integ. tests unit test (system) (black (white
box) box)
when is testing complete?One model:"logarithmic Poisson model”
f(t)=(1/p)ln(I0pt+1)f(t) = cumulative expected failures at time tI0 = failures per time unit at beginning of testingp = reduction rate in failure intensity
START
END
Requirements, Specs/System Tests
Design/Integration Tests
Code/Unit Tests
Design/Module Tests
Development and Testing Stages
levels of test development stage white or glass box code black box class integration class (ER) diagram system use case
We will use these stages for the quarter project.
We will use a modified XP strategy:
----develop test with design at each stage
----during implementation, all tests must be passed (100%)
----if modifications are made, all tests must be rerun
----if errors are found, new tests must be written to cover them (“regression testing”)
----complete test suite, updated during development, must be maintained
Types of testing
Types of testing:
white box--"internals” (also called "glass box")
black box—modules and their "interfaces” (also called "behavioral")
system--”functionality” (can be based on specs, use cases)
application-specific--GUIsClient/ServerReal-time (e.g.: drug dosage monitor; thermostat)Documentation/help
Good testing strategy
steps in good test strategy:
• quantified requirements
• test objectives explicit
• user requirements clear
• use "rapid cycle testing"
• build self-testing software
• filter errors by technical reviews
• review test cases and strategy formally also
• continually improve testing process
OO testing strategy
OO testing:
• emphasis is on interfaces
• use UML tools to support testing strategies and development of test cases
--system tests: use cases; quality measurements--black box tests: ER diagrams, object message diagrams,dataflow and state diagrams--white box tests: class and state diagrams, CRC cards
Using specifications for system tests
System tests should verify that specifications have been met
For UML-based strategy:
each use case ---> one or more system tests
each quality / performance requirement
one or more system tests
Additional qualitative or quantitative tests (not from use cases):
examples: is system “user-friendly”?
are timing requirements met?
are available resources sufficient?
Using specifications for system tests
Example:
1. Place call
2. Receive call
3. Use scheduler
Cellular network
User
Associated sequence diagrams1.2.3.
Associated test cases1.2.3.
3 use cases Tests verify use case supported
Black box testing--what to test
black box testing: test functional requirements of components.
Must check:
incorrect or missing components
interface errors
data structures or external data access
behavior /performance errors
initialization and termination errors
Black box testing--testing graph
start point is usually a graph:
•objects to be modeled
•relationships connecting them ("links")
•link properties
example: can use ER diagrams, object message diagrams, state diagrams, with additional information on links as necessary
Black box testing--examples
Examples:
Car GasStation:station
P
company
employee
Denotes link that leads to one or more test cases
Black box testing techniques
Some useful techniques for black box testing:
•transaction flow
•data flow
•state modeling
•timing modeling
(all "dynamic")
much testing focuses on "boundary values" between components
Black box testing--input partitioning
example: equivalence partitioning for input for black box test:
condition # ”cases” of input
Range 1 valid, 2 invalidexample: 0 < x < 10; test x = ?
value 1 valid, 2 invalidexample: y = 7; test y = ?
set member 1 valid, 1 invalidexample: j is even; test j = ?
boolean 1 valid, 1 invalid
Black box testing guidelines
General guidelines:
test BOUNDARIES
test output also
choose "orthogonal” cases if possible
not
White box testing
White box testing: we will look at specific strategies later on (e.g., path testing)