test: add coverage for uncovered if statement in fs.read function(callback and promise api)

[mayankagarwals]

Expanded coverage of tests as my first contribution to nodejs:). It would be really helpful if other contributors can point out any errors I have made and/or good practices I am missing!.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes

[Trott]

Welcome @iammack and thanks for the pull request.

Is this the line you're adding coverage for?

https://coverage.nodejs.org/coverage-09af8c822c8e931b/lib/fs.js.html#L514

If so, we probably also want to test that it works when offset is undefined.

[mayankagarwals]

Glad to be contributing:)

Yes, that line and this line: https://coverage.nodejs.org/coverage-642f2064c06793b7/lib/internal/fs/promises.js.html#L326.

Actually, the test when offset is undefined has been implemented in https://github.com/nodejs/node/blob/master/test/parallel/test-fs-read-optional-params.js but this test just compares the length of the returned buffer and not its contents. Is that a good enough test? If not, wouldn't it be better to change the optional-params file itself to include a check for contents so that the change would cover other parameters of fs.read too making tests for all the conditions stronger?

[mayankagarwals]

Not sure what's the equivalent of "bringing this to the top of your inbox" in GitHub :p. So gentle ping @Trott

[Trott]

I'm surprised that setting offset to undefined doesn't cover the same line, but I also didn't look that closely. Further improvements are welcome, please don't let me stop you, but this is good enough to land. Thanks.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/34432/

[Trott]

Landed in 0027aca