Run code coverage for a single file

[wnordmann]

The directions for running code coverage do not detail how to run coverage for a single file. It would improve performance when writing tests with the goal of improving coverage to be able to test one file at a time.
https://github.com/nodejs/node/blob/master/doc/guides/contributing/pull-requests.md#test-coverage

[addaleax]

/cc @bcoe

[mhdawson]

@wnordmann if I understand correctly you want to just get the coverage provided by running a single test?

[wnordmann]

@mhdawson correct. The main goal is a document update allowing for quick testing / verifying of code coverage.

[mhdawson]

@wnordmann can you try out this branch https://github.com/mhdawson/io.js/tree/cov-single

It has an additional target coverage-update which might be what you want.

You would use as follows

1. run make coverage normally
2. Make your updates to specific tests, run those specific tests
3. run coverage-update
4. Review the updated coverage.

I think it would update overall coverage based on only the tests you have run.

[mhdawson]

If that works for you I'll PR it in.

[bcoe]

@mhdawson @wnordmann sorry for dropping this thread on the floor; Not going to lie, I was making an effort to get #23941 over the finish line (which has the potential to significantly simplify coverage collecting.

Once #23941 lands, collecting coverage for a single file becomes as simple as:

NODE_V8_COVERAGE=./cov ./tools/test.py parallel/test-fs-mkdir.js
c8 report --temp-dir=./cov --resolve=./lib --reporter=html --omit-relative-false

[wnordmann]

I appreciate the two solutions to the problem. I'll hold out and test with #23941 once it lands.

[antsmartian]

@wnordmann : #23941 landed. So you are still gonna work on this? I just tried playing around and looks like the following command does generates the coverage:

NODE_V8_COVERAGE=./cov ./tools/test.py parallel/test-fs-mkdir.js
c8 report --temp-directory=./cov --resolve=./lib --reporter=html

However, the index.html which was generated just shows the empty page, but the corresponding lib/<file> does shows the coverage for the given test case. @bcoe Anything I'm missing here?

[bcoe]

@wnordmann @antsmartian please try:

d1dee49

which was just landed; it has new instructions.

[jasnell]

I believe this is resolved or not further actionable. Closing. Can reopen if necessary