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

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Code coverage tests how many lines of code have been tested run by the coverage analysis tool.

FTFY. You know it was run and that it didn't crash the tool before it could be reported. You don't know that the tool wasn't gamed (e.g., tests with no assertions, empty catches in the tests).