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Black Box Unit Testing

Black Box Unit Testing. 1209. What is black-box testing?. Unit (code, module) seen as a black box No access to the internal or logical structure Determine if given input produces expected output. Output. Input. Black Box Testing. Test set is derived from requirements

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Black Box Unit Testing

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  1. Black Box Unit Testing 1209

  2. What is black-box testing? • Unit (code, module) seen as a black box • No access to the internal or logical structure • Determine if given input produces expected output. Output Input

  3. Black Box Testing • Test set is derived from requirements • Goal is to cover the input space • Lots of approaches to describing input space: • Equivalence Classes • Boundary Value Analysis • Decision Tables • State Transitions • Use Cases • . . .

  4. Advantage and Disadvantage • Advantage: • Disadvantage: • Need to define an efficient strategy to limit number of test cases

  5. General Black Box Process • Analyze requirements • Select valid and invalid inputs • Determine expected outputs • Construct tests • Run tests • Compare actual outputs to expected outputs

  6. Equivalence Relations: • Reflexive • Symmetric • Transitive

  7. Equivalence classes: Basic Strategy • Partition the input into equivalence classes • Test a subset from each class

  8. Basic strategy: Example: fact(n): if n<0, or n>=200 error if 0<=n<=20, exact value if 20<n<200, approximate value within .1%

  9. Simple Example: • Suppose you are building an airline reservation system. A traveler can be a child, an adult, or a senior. • The price depends on the type of traveler. • The seat reservation does not depend on the type of traveler. • How many test cases are required for the reservation component and the billing component?

  10. Finding equivalence classes: • Identify restrictions for inputs and outputs in the specification • If there is a continuous numerical domain, create one valid and two or three invalid classes (above, below, and NaN) • If a number of values is required, create one valid and two invalid classes

  11. Boundary Values: • Programs that fail at interior elements of a class usually fail at the boundaries too. • Test the boundaries.

  12. Hints • If a domain is a restricted set, check the boundaries. e.g., D=[1,10], test 0, 1, 10, 11 • It may be possible to test the boundaries of outputs, also. • For ordered sets, check the first and last elements • For complex data structures, the empty list, full lists, the zero array, and the null pointer should be tested

  13. Boundary Value: in class • Determine the boundary values for US Postal Service ZIP codes • Determine the boundary values for a 15- character last name entry.

  14. Decision Tables • Construct a table (to help organize the testing) • Identify each rule or condition in the system that depends on some input • For each input to one of these rules, list the combinations of inputs and the expected results

  15. Decision Table Example Theater ticket prices are discounted for senior citizens and students.

  16. Pairwise Testing

  17. Problem 1From Lee Copeland, A Practitioner’s Guide to Software Test Design, Artech House Publishers, 2004. • A web site must operate correctly with different browsers: IE 5, IE 6, and IE 7; Mozilla 1.1; Opera 7; and FireFox 2, 3, and 4. • It must work using RealPlayer, MediaPlayer, or no plugin. • It needs to run under Windows ME, NT, 2000, XP, and Vista, and 7.0 • It needs to accept pages from IIS, Apache and WebLogic running on Windows NT, 2000, and Linux servers

  18. Problem 2 From Lee Copeland, A Practitioner’s Guide to Software Test Design, Artech House Publishers, 2004. • A bank is ready to test a data processing system • Customer types • Gold (i.e., normal) • Platinum (i.e., important) • Business • Non profits • Account types • Checking • Savings • Mortgages • Consumer loans • Commercial loans • States (with different rules): CA, NV, UT, ID, AZ, NM

  19. When given a large number of combinations: (options improve …) • Give up and don’t test • Test all combinations … miss targets, delay product launch, and go out of business • Choose one or two cases

  20. Orthogonal Arrays • A 2-D array with the property • All pairwise combinations occur in every pair of columns • Example: consider 3 variables (columns) with {a,b}, {1,2}, and (α,β)

  21. Orthogonal Array Example Look at each pair of columns (1 and 2),( 1 and 3), and (2 and 3) Does each of the 4 pairings appear in each? (Yes, of course!)

  22. Pairwise Testing Algorithm • Identify variables • Determine choices for each variable • Locate an orthogonal array • Map test cases to the orthogonal array • Construct tests

  23. Example using Bank • Identify variables • Determine choices for each variable • Locate an orthogonal array • Map test cases to the orthogonal array • Construct tests

  24. Locate an orthogonal array (look up on web)

  25. Map Test Cases (30)

  26. Pairwise Summary • When the combination is large, test all pairs, not all combinations • Studies indicate that most defects are single or double-mode effects • Can be found in pairing • Few defects require more than two modes • Orthogonal arrays have the pairwise property and can be found or generated

  27. State Transition Testing

  28. State Transition Testing • Build STD of system or component • Cover the STD

  29. Example Payment made Ticket Printed Paid Res Made Ticketed Cancel Cancel/refund Cust Order/start timer Time Expires Cancelled Cust Cancelled Non Pay Ticket Delivered Cancel/refund Used

  30. Use Case Testing

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