estimating of testing effort as a percentage of development time

Question

Does anyone use a rule of thumb basis to estimate the effort required for testing as a percentage of the effort required for development  And if so what percentage do you use

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Some years ago  in a safety critical field  I have heard something like one day for unit testing ten lines of code   I have also observed 50  of effort for development and 50  for testing  not only unit testing

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From my experience  25  effort is spent on Analysis  50  for Design  Development and Unit Test  remaining 25  for testing  Most projects will fit within a   -10  variance of this rule of thumb depending on the nature of the project  knowledge of resources  quality of inputs  amp  outputs  etc  One can add a project management overhead within these percentages or as an overhead on top within a 10-15  range

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Gartner in Oct 2006 states that testing typically consumes between 10  and 35  of work on a system integration project   I assume that it applies to the waterfall method   This is quite a wide range - but there are many dependencies on the amount of customisations to a standard product and the number of systems to be integrated

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Judge by yesterday s weather  How long did it take last time  Are you trending longer or shorter  Each shop is different    Most agile shops need a lot less time  have drastically fewer defects  and quicker time to resolve them because of TDD  Even so  most agile shops have some measurable time spent with testing QC     If this is the first test run for this application  then the answer is  lets see  followed by an attempt   It depends on how quick you can get questions answered    - how testable it is   - how many features functions  - how many defects are discovered   - how quickly issues are resolved   - how many times the code cycles    through testing  and  - how many times testing is blocked by    bugs  There is no way to tell  You could call it 50  or 175  or more  and not be wrong  Why not make a rough guess and multiply by Pi  It won t be much worse than any other answer you can make up   You should  must  know how long it takes now and whether it s getting faster or slower  and whether the coverage is increasing or decreasing  With those three bits of information  you should be able to guess quite well

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Are you talking about automated unit integration tests or manual tests   For the former  my rule of thumb  based on measurements  is 40-50  added to development time i e  if developing a use case takes 10 days  before an QA and serious bugfixing happens   writing good tests takes another 4 to 5 days - though this should best happen before and during development  not afterwards

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The Google Testing Blog discussed this problem recently      So a naive answer is that writing test carries a 10  tax  But  we pay taxes in order to get something in return      snip      These benefits translate to real value today as well as tomorrow  I write tests  because the additional benefits I get more than offset the additional cost of 10   Even if I don t include the long term benefits  the value I get from test today are well worth it  I am faster in developing code with test  How much  well that depends on the complexity of the code  The more complex the thing you are trying to build is  more ifs loops dependencies  the greater the benefit of tests are

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When you speak of tests  you could mean waterfall or agile test development   In an agile environment  developers should spend 50  of their time developing and maintaining tests     But that 50  extra will save you time when the re-factoring and manual verification time comes

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Testing time is probably more closely correlated to feature scope than development time   I d also argue  perhaps controversially  that testing time is correlated to the skill of your development team   For a 6-to-9 month development effort  I demand a absolute minimum of 2 weeks testing time  performed by actual testers  not the development team  who are well-versed in the software they will be testing  i e   2 weeks does not include ramp-up time    This is for a project that has  5 developers

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The only time I factor in extra time for testing is if I m unfamiliar with the testing technology I ll be using  e g  using Selenium tests for the first time    Then I factor in maybe 10-20  for getting up to speed on the tools and getting the test infrastructure in place   Otherwise testing is just an innate part of development and doesn t warrant an extra estimate   In fact  I d probably increase the estimate for code done without tests   EDIT  Note that I m usually writing code test-first  If I have to come in after the fact and write tests for existing code that s going to slow things down   I don t find that test-first development slows me down at all except for very exploratory  read  throw-away  coding

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When you re estimating testing you need to identify the scope of your testing - are we talking unit test  functional  UAT  interface  security  performance stress and volume    If you re on a waterfall project you probably have some overhead tasks that are fairly constant  Allow time to prepare any planning documents  schedules and reports   For a functional test phase  I m a  system tester  so that s my main point of reference  don t forget to include planning  A test case often needs at least as much effort to extract from requirements   specs   user stories as it will take to execute  In addition you need to include some time for defect raising   retesting  For a larger team you ll need to factor in test management - scheduling  reporting  meetings    Generally my estimates are based on the complexity of the features being delivered rather than a percentage of dev effort  However this does require access to at least a high-level set of instructions  Years of doing testing enables me to work out that a test of a particular complexity will take x hours of effort for preparation and execution  Some tests may require extra effort for data setup  Some tests may involve negotiating with external systems and have a duration far in excess of the effort required    In the end  though  you need to review it in the context of the overall project  If your estimate is well above that for BA or Development then there may be something wrong with your underlying assumptions    I know this is an old topic but it s something I m revisiting at the moment and is of perennial interest to project managers

[testing] estimating of testing effort as a percentage of development time

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