>The assertion has been made that typical applications have between 40%-50% of their code actually run during testing.
>
>I am curious to see what percentage of code you test (actually run during development/unit test/system testing) for:
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>1) The development of a system from scratch.
>

60-70% But this is a wild guess since we don't have statistics to back this. All our programmers have the responsiblity of testing as much of their code as possible. We also have a second team of testing repeating all the tests, All changes are tested a third time with our final test plan.

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>2) The development of a new/replacement system but using code parts (including classes, functions, etc.) from existing and well-running systems.
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60-70% Again with no real stat to prove it.

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>3) Developing revisions to an existing application.

40-50% And we have stats to prove it. Don't beleive we are careless in testing our releases. We have a very strict regression test plan and also test every modified functions but only 40-50% of all lines of code get executed.

A large part of most code in most apps is coded for exception handling, user errors, validation etc... Without forgetting all branches of cases, if, while, for loop etc... So I figure out 40-50% is a fair number for release testing.