Using UML Patterns and Java ObjectOriented Software Engineering
Using UML, Patterns, and Java Object-Oriented Software Engineering Chapter 11, Testing
Outline ¨ ¨ ¨ Terminology Types of errors Dealing with errors Quality assurance vs Testing Component Testing ¨ System testing w w w Function testing Structure Testing Performance testing Acceptance testing Installation testing w Unit testing w Integration testing ¨ ¨ Testing Strategy Design Patterns & Testing Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 2
Terminology ¨ ¨ ¨ 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. Error: 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. Correction: a change to a component whose purpose is to repair a fault There are many different types of errors and different ways how we can deal with them. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 3
Quality of today’s software…. The average software product released on the market is not error free. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 4
Model elements used during testing A part of the system that can be isolated for testing (an object, a group of objects, a subsystem) Test suite is revised by exercises * 1…n * Test case Component Correction * * * Test stub finds repairs * Test driver * Failure * * * is caused by Error * * Fault is caused by A design or coding mistake that A deviation between the A set of inputs and expected A manifestation results of a fault causes abnormal component specification and the actual Bernd exercises Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java that a component during the execution behavior 5 behavior
What is this? A failure? (malfunzionamento) An error? A fault? (difetto) Need to specify the desired behavior first! Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 6
Erroneous State (“Error”) Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 7
Algorithmic Fault Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 8
Mechanical Fault Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 9
Terminology 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. ¨ Error: 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. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 10
How do we deal with Errors and Faults? Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 11
Verification? Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 12
Modular Redundancy? Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 13
Declaring the Bug as a Feature? Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 14
Patching? Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 15
Testing? Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 16
Examples of Faults and Errors ¨ Faults in the Interface specification w Mismatch between what the client needs and what the server offers w Mismatch between requirements and implementation ¨ Algorithmic Faults w Missing initialization w Branching errors (too soon, too late) w Missing test for nil Bernd Bruegge & Allen H. Dutoit ¨ Mechanical Faults (very hard to find) w Documentation does not match actual conditions or operating procedures ¨ Errors w w Stress or overload errors Capacity or boundary errors Timing errors Throughput or performance errors Object-Oriented Software Engineering: Using UML, Patterns, and Java 17
Dealing with Errors ¨ Verification: w Assumes hypothetical environment that does not match real environment w Proof might be buggy (omits important constraints; simply wrong) ¨ Modular redundancy: w Expensive ¨ Declaring a bug to be a “feature” w Bad practice ¨ Patching w Slows down performance ¨ Testing (this lecture) w Testing is never good enough Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 18
Another View on How to Deal with Errors ¨ Error prevention (before the system is released): w Use good programming methodology to reduce complexity w Use version control to prevent inconsistent system w Apply verification to prevent algorithmic bugs ¨ Error detection (while system is running): w Testing: Create failures in a planned way w Debugging: Start with an unplanned failures w Monitoring: Deliver information about state. Find performance bugs ¨ Error recovery (recover from failure once the system is released): w Data base systems (atomic transactions) w Modular redundancy w Recovery blocks Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 19
Some Observations ¨ It is impossible to completely test any nontrivial module or any system w Prohibitive in time and cost ¨ Testing can only show the presence of bugs, not their absence (Dijkstra) Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 20
Testing takes creativity ¨ ¨ Testing often viewed as dirty work. To develop an effective test, one must have: t t t ¨ 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 w We often develop a certain mental attitude that the program should be in a certain way when in fact it does not. ¨ Programmer often stick to the data set that makes the program work w "Don’t mess up my code!" ¨ A program often does not work when tried by somebody else. w Don't let this be the end-user. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 21
Testing Activities Subsystem Code Unit Tested Subsystem Requirements Analysis Document System Design Document Integration Test Integrated Subsystems Functional Test User Manual Functioning System Tested Subsystem Code Unit Test Bernd Bruegge & Allen H. Dutoit All tests by developer Object-Oriented Software Engineering: Using UML, Patterns, and Java 22
Testing Activities continued Client’s Understanding of Requirements Global Requirements Validated Functioning System Performance. System Test Accepted System Acceptance Test User Environment Installation Tests by client Tests by developer User’s understanding Tests (? ) by user Bernd Bruegge & Allen H. Dutoit Usable System Object-Oriented Software Engineering: Using UML, Patterns, and Java System in Use 23
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 Bernd Bruegge & Allen H. Dutoit Integration Testing System Testing Correctness Debugging Object-Oriented Software Engineering: Using UML, Patterns, and Java Performance Debugging 24
Types of Testing ¨ Unit Testing: w Individual subsystem w Carried out by developers w Goal: Confirm that subsystems is correctly coded and carries out the intended functionality ¨ Integration Testing: w Groups of subsystems (collection of classes) and eventually the entire system w Carried out by developers w Goal: Test the interface among the subsystem Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 25
System Testing ¨ System Testing: w The entire system w Carried out by developers w Goal: Determine if the system meets the requirements (functional and global) ¨ Acceptance Testing: w Evaluates the system delivered by developers w Carried out by the client. May involve executing typical transactions on site on a trial basis w Goal: Demonstrate that the system meets customer requirements and is ready to use ¨ Implementation (Coding) and testing go hand in hand Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 26
Unit Testing ¨ Informal: w Incremental coding ¨ Static Analysis: w w ¨ Hand execution: Reading the source code Walk-Through (informal presentation to others) Code Inspection (formal presentation to others) Automated Tools checking for t syntactic and semantic errors t departure from coding standards Dynamic Analysis: w Black-box testing (Test the input/output behavior) w White-box testing (Test the internal logic of the subsystem or object) w Data-structure based testing (Data types determine test cases) Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 27
The test case It is a set of input data and expected results that exercises a component with the purpose of causing failures and detecting faults. Attributes of the test case: w Name t it allows the designer to distinguish different test cases w Location t where the test case is located; it could address the pathname or the URL of the executable and input data w Input t the set of input data w Oracle t the expected behavior of the component (the set of output data/ commands that the system should provide) w Log t a set of time-stamped correlations of the observed and expected behavior (for various test runs) Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 28
Black-box Testing ¨ Focus: I/O behavior. If for any given input, we can predict the output, then the module passes the test. w Almost always impossible to generate all possible inputs ("test cases") ¨ Goal: Reduce number of test cases by equivalence partitioning: w Divide input conditions into equivalence classes t System is supposed to behave in the same way for all the members (inputs) of the class w Choose test cases for each equivalence class. t t Example: If an object is supposed to accept a negative number, testing one negative number is enough Criteria: – Coverage: every possible input belongs to one of the equivalence classes – Disjointedness: No input belongs to more than one equivalence class – Representation: If the execution demonstrates and error with a particular member, the same error will be detected using any other member of the class Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 29
Unit testing: Black-box Testing (Continued) Equivalence Testing ¨ Selection of equivalence classes (No rules, only guidelines): 1. Input is valid across range of values Select test cases from 3 equivalence classes: t t t Below the range Within the range Above the range 2. Input is valid if it is from a discrete set Select test cases from 2 equivalence classes: t t ¨ Valid discrete value Invalid discrete value Another solution to select only a limited amount of test cases: w Get knowledge about the inner workings of the unit being tested => white-box testing Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 30
Unit testing: Boundary Testing ¨ ¨ A special case of equivalence testing Focuses on the conditions at the boundary of the equivalence class w 0, empty strings, year 2000 ¨ Problem: Equivalence and Boundary testing do not explore combinations of test input data w Sometimes a program fails because of a combination of values, not because of the single one Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 31
White-box Testing ¨ ¨ Focus: Thoroughness (Coverage). Every statement in the component is executed at least once. Four types of white-box testing w Path Testing (all paths in the program are executed , see next slides) w Statement Testing (Tests single statements) w Loop Testing (Focuses on loops: skip, execute once, execute more than once) w Branch Testing (Each possible outcome from a condition is tested at least once) w State-based testing (Derives test cases from the state-chart of the class) Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 32
White-box Testing (Continued) ¨ ¨ Statement Testing (Algebraic Testing): Test single statements (Choice of operators in polynomials, etc) Loop Testing: w Cause execution of the loop to be skipped completely. (Exception: Repeat loops) w Loop to be executed exactly once w Loop to be executed more than once ¨ Path testing: w 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("YESn"); else printf("NOn"); Test cases: 1) i = TRUE; 2) i = FALSE Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 33
White-box Testing Example Find. Mean(float Mean, FILE Score. File) { Sum. Of. Scores = 0. 0; Number. Of. Scores = 0; Mean = 0; Read(Score. File, Score); /*Read in and sum the scores*/ while (! EOF(Score. File) { if ( Score > 0. 0 ) { Sum. Of. Scores = Sum. Of. Scores + Score; Number. Of. Scores++; } Read(Score. File, Score); } /* Compute the mean and print the result */ if (Number. Of. Scores > 0 ) { Mean = Sum. Of. Scores/Number. Of. Scores; printf("The mean score is %f n", Mean); } else printf("No scores found in filen"); } Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 34
White-box Testing Example: Determining the Paths Find. Mean (FILE Score. File) { float Sum. Of. Scores = 0. 0; int Number. Of. Scores = 0; 1 float Mean=0. 0; float Score; Read(Score. File, Score); 2 while (! EOF(Score. File) { 3 if (Score > 0. 0 ) { Sum. Of. Scores = Sum. Of. Scores + Score; Number. Of. Scores++; } 5 Read(Score. File, Score); 4 6 } /* Compute the mean and print the result */ 7 if (Number. Of. Scores > 0) { Mean = Sum. Of. Scores / Number. Of. Scores; printf(“ The mean score is %fn”, Mean); } else printf (“No scores found in filen”); 9 } Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 8 35
Constructing the Logic Flow Diagram Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 36
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 Bernd Bruegge & Allen H. Dutoit 3 Exit l Object-Oriented Software Engineering: Using UML, Patterns, and Java 37
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 Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 38
Unit testing: white box testing: State based testing ¨ ¨ Introduced for OO programs It looks at the state machine of each class w The aim is comparing the actual state of the class with the expected one w Test cases are derived from the UML statechart of the class w For each state a representative set of stimuli is derived for each transition (like in the equivalence testing). Then the variables of the class are observed to verify that the class has reached the specified state ¨ Not very used (yet) Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 39
Comparison of White & Black-box Testing ¨ White-box Testing: ¨ w Potentially infinite number of paths have to be tested w White-box testing often tests what is done, instead of what should be done w Cannot detect missing use cases ¨ Black-box Testing: w Potential combinatorial explosion of test cases (valid & invalid data) w Often not clear whether the selected test cases uncover a particular error w Does not discover unknown (to tester) use cases ("features") Bernd Bruegge & Allen H. Dutoit ¨ ¨ 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: w w Number of possible logical paths Nature of input data Amount of computation Complexity of algorithms and data structures Object-Oriented Software Engineering: Using UML, Patterns, and Java 40
The 4 Testing Steps 1. Select what has to be measured 3. Develop test cases w Analysis: Completeness of requirements w Design: tested for cohesion w Implementation: Code tests 2. Decide how the testing is done w w Code inspection Black-box, white box, Proofs (Design by Contract) Select integration testing strategy (big bang, bottom up, top down, sandwich) Bernd Bruegge & Allen H. Dutoit w 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 w An oracle contains of the predicted results for a set of test cases w The test oracle has to be written down before the actual testing takes place Object-Oriented Software Engineering: Using UML, Patterns, and Java 41
Guidance for Test Case Selection ¨ Use analysis knowledge about functional requirements (black-box testing): w Use cases w Expected input data w Invalid input data ¨ ¨ Use implementation knowledge about algorithms: w Examples: w Force division by zero w Use sequence of test cases for interrupt handler Use design knowledge about system structure, algorithms, data structures (white-box testing): w Control structures t Test branches, loops, . . . w Data structures t Test records fields, arrays, . . . Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 42
Unit-testing Heuristics 1. Create unit tests as soon as object design is completed: w Black-box test: Test the use cases & functional model w White-box test: Test the dynamic model w Data-structure test: Test the object model 2. Develop the test cases w Goal: Find the minimal number of test cases to cover as many paths as possible 3. Cross-check the test cases to eliminate duplicates w Don't waste your time! Bernd Bruegge & Allen H. Dutoit 4. Desk check your source code w Reduces testing time 5. Create a test harness w Test drivers and test stubs are needed for integration testing 6. Describe the test oracle w Often the result of the first successfully executed test 7. Execute the test cases w Don’t forget regression testing w Re-execute test cases every time a change is made. 8. Compare the results of the test with the test oracle w Automate as much as possible Object-Oriented Software Engineering: Using UML, Patterns, and Java 43
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