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Code Coverage Ignore Comments

c8 is my preferred package for calculating code coverage in Node.js testing and it is also apparently used by web-test-runner. However, c8 supports a lot more ignore comments then they document. Below I've listed all the supported comments from my own personal testing and some other notes about ignoring lines for code coverage.

tl;dr, use these comments.

  • For reasonable sized blocks of ignored code, use /* node:coverage ignore next <line-count> */.
  • For long blocks of ignored code, wrap the block in /* node:coverage disable */ and /* node:coverage enable */.

These recommended comments allow you to avoid the most problems and support the widest range of tools. (Specifically, they are supported by c8, web-test-runner, and Node.js's built-in test runner).

Comments that work​

All of these comments will work with both Node.js tests using c8 and web-test-runner browser tests.

  • "c8" comments
    • /* c8 ignore next */
    • /* c8 ignore next <line-count> */
    • /* c8 ignore start */
    • /* c8 ignore stop */
  • "v8" comments
    • /* v8 ignore next */
    • /* v8 ignore next <line-count> */
    • /* v8 ignore start */
    • /* v8 ignore stop */
  • "node:coverage" comments
    • /* node:coverage ignore next */
    • /* node:coverage ignore next <line-count> */
    • /* node:coverage disable */
    • /* node:coverage enable */

Comments that don't work​

  • single line comments don't work
    • // c8 ignore next
    • // c8 ignore next <line-count>
    • // c8 ignore start
    • // c8 ignore stop
    • // v8 ignore next
    • // v8 ignore next <line-count>
    • // v8 ignore start
    • // v8 ignore stop
    • // node:coverage ignore next
    • // node:coverage ignore next <line-count>
    • // node:coverage disable
    • // node:coverage enable
  • /* istanbul ignore next */: istanbul comments are not supported
  • /* c8 ignore next <block name> */: block name ignore comments are not supported (as opposed to istanbul which does support this)
  • /* node:coverage ignore start */: use /* node:coverage disable */
  • /* node:coverage ignore stop */: use /* node:coverage enable */
  • /* c8 disable */: use /* c8 ignore start */
  • /* c8 enable */: use /* c8 ignore stop */

Issues to keep in mind​

  • The "ignore next" comments (without a line count) are very inconsistent and unpredictable. I've also found that sometimes those comments themselves get marked as missing coverage!
  • Node's built-in test runner with coverage (node --test --experimental-test-coverage) does not support any of the "v8" or "c8" comments, only the node:coverage comments.