Comment by smarx007

7 hours ago

I think the phase change hypothesis* is a bit wrong.

I think it happens not at 100% coverage but at, say, 100% MC/DC test coverage. This is what SQLite and avionics software aim for.

*has not been confirmed by a peer-reviewed research.

7 comments

smarx007

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cloudhead  7 hours ago

What's MC/DC?

  • smarx007  6 hours ago

    Modified Condition/Decision Coverage (MC/DC) is a test coverage approach that considers a chunk of code covered if:

    - Every branch was "visited". Plain coverage already ensures that. I would actually advocate for 100% branch coverage before 100% line coverage.

    - Every part (condition) of a branch clause has taken all possible values. If you have if(enabled && limit > 0), MC/DC requires you to test with enabled, !enabled, limit >0, limit <=0.

    - Every change to the condition was shown to somehow change the outcome. (false && limit > 0) would not pass this, a change to the limit would not affect the outcome - the decision is always false. But @zweifuss has a better example.

    - And, of course, every possible decision (the outcome of the entire 'enabled && limit > 0') needs to be tested. This is what ensures that every branch is taken for if statements, but also for switch statements that they are exhaustive etc.

    MC/DC is usually required for all safety-critical code as per NASA, ESA, automotive (ISO 26262) and industrial (IEC 61508).

    • amarant  2 hours ago

      Limit <=0 appears to include every number between 0 and INT_MIN.

      I hope you don't have any string inputs, or your test is gonna take a while to run!

      1 reply →

  • zweifuss  6 hours ago

    Modified Condition/Decision Coverage

    It's mandated by DO-178C for the highest-level (Level A) avionics software.

    Example: if (A && B || C) { ... } else { ... } needs individual tests for A, B, and C.

    Test #,A,B,A && B,Outcome taken,Shows independence for

    1,True,True,True,if branch,(baseline true)

    2,False,True,False,else branch,A (A flips outcome while B fixed at True)

    3,True,False,False,else branch,B (B flips outcome while A fixed at True)

  • emoII  6 hours ago

    Basically branch coverage but also all variations of the predicates, e.g. testing both true || true, and true || false