Download - Class Testing Software Engineering of Standalone Programs University of Colorado, Boulder
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Overview Class Testing Testing Interactions between objects Testing Class Hierarchies
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Basics – How to test a single class
Class Testing How to Test a Class Aspects of Class Testing How to Construct Test Cases When is a class test suite adequate? How to Construct a Test Driver
Testing Interactions between objects Testing Class Hierarchies
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Definition of class testing Verifying implementation of a class = verifying the
specification for that class
If so, each of the instances should behave properly.
Assumption: The class in question has a complete and
correct specification that has been tested earlier in the context of models
Spec is expressed in natural language or as a state transition diagram
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Ways to test a class Code can be tested effectively by
inspection (preferable when construction of a test driver is too difficult)
execution of test cases (lends itself to easy regression testing later on)
Remember: When you test a class, you are really: creating instances of that class and testing the behavior of those instances.
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Aspects of Class Testing
Decide test independently test as a component of a larger part of the
system How decide – combination of the following:
Role of the class in the system – degree of risk Complexity of the class Amount of effort associated with developing a
test driver Sometimes, needs so many collaborators,
makes more sense to test in a cluster
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Who Tests? How much?
Who – class usually tested by its developer Understands class’ spec Familiar with the code Test driver can be used by the developer to
debug code while writing it but ... perpetuates misunderstanding – needs
inspection at model stage to head that off What – ensure that the code for a class exactly
meets the requirements – no more, no less
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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When are tests written?
When – A test plan that identifies test cases should be developed soon after a class is fully specified and ready for coding. Especially if developer is the class tester Why?
(What’s the danger in developer alone writing and reviewing test cases for the class?)
When again? Iterative development – the driver and the test
cases will be available to supplement or change as the class is enhanced or modified
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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How can you test “just a class”?
How – Create a test driver that
creates instances of the class sets up a suitable environment around those
instances to run a test case sends one or more messages to an instance
as specified by a test case checks the outcome based on a reply value,
changes to the instance, or parameters to the message
deletes any instances it creates if responsible for storage allocation
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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How do we test static data in a class?
How – continued: Static data members or operations
testing required they belong to the class itself rather than to
each instance of the class the class can be treated as an object
If the behavior of the instances of a class is based on the values of class-level attributes test cases for testing the class-level attributes
must be considered as an extension of the state of the instances
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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How MUCH testing is done at this level?
How much – Adequacy of testing measured in terms of how much of the specification has been tested how much of the implementation has been
tested Want to test operations and state transitions in
many combinations Objects maintain state. “State” affects the
meaning of operations.
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Constructing test cases - identification
Identification of test cases Should be made from the specification that has
been reviewed rather than from the implementation which may embody developer’s misunderstandings
Best: develop from spec and augment to test boundaries introduced by the implementation
If no spec exists: create one from the code and verify it with the developer
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Constructing test cases – identification2
Identify requirements for test cases for all possible combinations of situations in which a precondition can hold post conditions can be achieved
Create test cases for those requirements specific input values – typical and boundary determine correct outputs eliminate conditions that are not meaningful
Add test cases to show what happens when a precondition is violated
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Constructing Test Cases – from STD’s State Transition Diagrams
They show behavior associated with instances of a class
Each transition represents a requirement for one or more test cases
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Constructing test cases from STD’s 2
Suppose 6 transitions between states Plus 1 constructor and 2 destructors That makes 9 requirements
Select representative values Select boundary values on each side of a
transition If the transition is guarded, select boundary
values for the guard condition Boundary values are based on the range of
attribute values associated with a state
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Top-level Statechart for Elevator Control
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Adequacy of a Class Test Suite Ideally – exhaustively test each class Practically – impossible or too hard Worth it to exhaustively test some classes with
high risk Measures of adequacy to increase confidence that
we have tested enough state-based coverage constraint-based coverage
Constraints are pre and post conditions and the class invariant
code-based coverage
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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State-based coverage How many of the transitions in a state transition diagram
are covered by the test suite? “Covered” = touched at least once May reveal each transition was covered but test values
do not adequately cover value ranges If test cases were generated correctly from a state
transition diagram with typical values and good boundary values, the test cases will achieve adequate state-based coverage
If test cases were generated from pre- and post conditions, then it is useful to check them against the state transition diagram to ensure each transition is covered.
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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State-based coverage: object interaction Note how operations interact w.r.t. transitions
Current State
Input or event
Action Output Next State
Sa E1 O1 Sc
Sb E2 O2 Sc
Sc E3 Sd
Test cases for the transition from Sc to Sd may work if Sc was reached from Sa but not if Sc was reached from Sb. “State” is a function of history.
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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State-based coverage: transition pairs Concerning problem on previous page:
Check that the test cases cover all pairs of transitions in the state transition diagram.
In previous table, create test cases to test: SaSc and ScSd SbSc and ScSd
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Statechart for Elevator Control
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Hierarchical statechart for Elevator Control
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Constraint-based coverage How many pairs of pre- and post conditions have
been covered? Using the technique described earlier for
generating test cases from pre and post conditions, if one test case is generated to satisfy each requirement, then the test suite meets this measure
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Constraint-Based coverage: object interaction
For each operation opn that is not an accessor operation, identify the operations op1, op2, etc. for which
their preconditions are met when the post conditions for opn hold.
That is, post condition(opn) satisfies (>=) precondition(op1), etc.
Then execute test cases for operation sequences opn-op1, opn-op2, etc.
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Class Diagram
Elevator Elevator Doors
Timer
Elevator Button
Up Floor Button
Floor
1 1 1 1
1
11
11
m
0…n
0…n
Travels-to
Travels-from
Opens-Closes Controls
Controls
Contains
velocity: ±m/sposition: meters
floor: integeron: Boolean
open: Booleanclosed: Booleanjammed: Boolean
time: seconds
floor: integerposition: meterson: Boolean
Down Floor Button
1
1
Contains
on: Boolean
Light
1on: Boolean
1
Turns-on
1
Turns-on 1Turns-on
1
1
Elevator Controller
1
0…n
ControlsRequests-elevator-of
Indicates-arrival-to
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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How do we complete the class test? States do not correspond 1-1 to methods or to
classes so the state transition diagram gives a different perspective
We want to adequately test the class Test each state transition, better yet, the pairs Look at the class diagram and see which classes
send messages to it To create a driver to simulate each class
sending msgs to the class-under-test could be difficult
If you only test each association in this application, it may be a weak level of testing for that class
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Constraint coverage completes testing it
If you test class A calling every msg it can in class B, that’s more coverage but …
If you use existing classes to do that, it’s hard to get the right combination set up to make it happen
Alternative: Write a driver with sequences of messages to
access sequences of methods in the class you are testing.
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Which sequences??
Look at the post conditions of each method in the class you want to test
Look at preconditions of each Find sequences where
the Post(m1) >= pre(m2) the Post(m2) >= pre(m3) Send msgs to m1; m2; m3
Do this for all possible combinations
November 21, 2005 ECEN5543CSCI5548 Univ of Colorado -- Class Testing
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Completion check
See which associations were tested by comparing to the class diagram
See which state transitions were covered this way If some state transitions were missed or if some
post/pre condition pairs or associations were missed, add a few tests