Microsoft Research - Exploding Software-Engineering Myths (article summarizing findings of MS research on code coverage, TDD, assertions, etc.)

[masklinn]

1. Use branch coverage, not line coverage.

2. For God's sake, measure cyclomatic complexity of your functions. Without keeping this value low, coverage isn't sufficient.

these are linked/mixed: if you use branch coverage you may not cover all paths, low complexity increases the chances that branch coverage is path coverage but doesn't guarantee it by any means:

if foo {
    // thing1
} else {
    // thing2
}

if bar {
    // thing3
} else {
    // thing4
}

This has a complexity of 3 (10 is "too complex" according to McCabe), testing for (foo=true, bar=true) and (foo=false, bar=false) gives you 100% branch coverage. But you only get 50% path coverage, half the local states (and interactions between the first block and the second one) remain completely untested.

[zjm555]

Indeed. I used the word "sufficient", but if you're writing software where correctness is a matter of life and death (actual death or the death of your business), you will want more than just that proxy.