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Software Testing

Software Testing. Testing Levels ( McConnel ). Unit Testing Single programmer involved in writing tested code Component Testing Multiple programmers involved in writing test code Integration Testing Testing two or more independently developed, interacting modules together

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Software Testing

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  1. Software Testing

  2. Testing Levels (McConnel) • Unit Testing • Single programmer involved in writing tested code • Component Testing • Multiple programmers involved in writing test code • Integration Testing • Testing two or more independently developed, interacting modules together • Regression Testing • Use a set of tests that can be rerun when changes are made to the system

  3. Testing Transparency • White-box Testing • Tester has access to the code • Black-box Testing • Tester has no access to the code • Relies on functional descriptions

  4. Test Plan • Test plan consists of a set of tests and the expected results

  5. Code coverage • What parts of the code are actually executed by a test? • Statement coverage • What combinations of sections of code are executed by a test? • Conditional Coverage (all conditions are evaluated as true at least once and as false at least once)

  6. Boundary Values • Identify equivalence classes • Array declaration example: • Good test cases usually test the boundary values of inputs • Empty strings • Max number of array elements

  7. Finding Equivalence Classes:C++ Array Declaration

  8. Boundary-Value Analysis • Successful test cases frequently include values that are “directly on, above or beneath the edges of input equivalence classes and output equivalence classes.” (Myers) • Each edge of an equivalence class is subject to test • Result space is considered as well as input space

  9. Boundary-Value Analysis (Myers) • Write test cases for the ends of input ranges • Input range is [-1.0, 1.0] • Write cases for -1.0, 1.0, -1.0001, 1.0001 • Number of possible inputs is [1,255] • Write cases for 0, 1, 255, 256 • Write test cases for the ends of output ranges • Calculated SS Tax (FICA) is [$0,$6621.60] • Write cases that yield results: $0, $.01, $6621.60 , and $6621.61 • Number of possible output is [1,255] • Write cases for 0,1 255, 256 outputs • Use “your ingenuity” to search for other boundary conditions. • Boundaries are not always so obvious

  10. When to write tests? • “All in all, I think test-first programming is one of the most beneficial software practices to emerge during the past decade…” • Steve McConnell • If you have to write tests eventually anyway, why not write them first so they can be useful longer. • Detect bugs earlier • Think more about requirements • Think more about how others will use your code

  11. Research Results on Tests • Two studies • 80% of errors are found in 20% of the classes • 50% of errors are found in 5% of classes • Most of the cost of a system might be represented by a very small amount of code. • Error prone routines should be redesigned and/or re-implemented

  12. Characterizing Errors • 85% corrected within a single routine • Three most common causes of errors • Thin-domain knowledge • Fluctuating/Conflicting Requirements • Communication/Coordination Breakdown • Almost always the programmer’s fault • Typos/Spelling errors are very common • Three most expensive errors involved the change of a single character • ($1.6 Billion, $900 Million, $245 Million) • Misinterpretation of Design • 85% of errors can be fixed in a few hours • It pays to know where you make errors (personal process) and where your project makes errors

  13. Number of Errors to Expect • Industry average is estimated at 1-25 errors per 1000 lines of code • MS Applications Division gets 10-20/1000 lines in in-house tests: .5/1000 in released code. • Space shuttle claims 0 defects in 500,000 lines of code

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