&gt; Most of the coding problems would have been caught had unit tests been clearer and closer to 100% branch&#x2F;code coverage. It is amazing how many bugs lurk in the last 5% of testing.<p>Presumably, coverage starts with the low-hanging fruit (simple, linear code; heavily-exercised code like startup routines and main loops; etc.) and grows to encompass ever more unweildy, smelly, edge-case parts of the codebase.<p>Hence, by increasing code coverage, we&#x27;re boiling off the solvent of run-of-the-mill code, such that what remains uncovered gets an ever stronger concentration of hackery, unintelligibility and black magic. By 95% coverage, the bits remaining are those parts people don&#x27;t want to touch, so I&#x27;d expect the concentration of bugs to be highest there.<p>:)