Add mutation testing with Stryker (and restructure some files)

[WillGibson]

The intention is to help identify areas of the code not covered by tests so that we can start to remediate that and increase confidence in releases.

This is the state of play right now...

stryker run
...
------------------------|------------------|----------|-----------|------------|----------|----------|
                        | % Mutation score |          |           |            |          |          |
File                    |  total | covered | # killed | # timeout | # survived | # no cov | # errors |
------------------------|--------|---------|----------|-----------|------------|----------|----------|
All files               |  30.40 |   70.37 |      146 |         6 |         64 |      284 |        0 |
 index.js               |  67.56 |   70.37 |      146 |         6 |         64 |        9 |        0 |
 markdown-link-check.js |   0.00 |    0.00 |        0 |         0 |          0 |      275 |        0 |
------------------------|--------|---------|----------|-----------|------------|----------|----------|
07:45:15 (50460) INFO HtmlReporter Your report can be found at: file:///Users/will.gibson/Dev/tcort/markdown-link-check/reports/mutation/mutation.html
07:45:15 (50460) INFO MutationTestExecutor Done in 3 minutes 37 seconds.

[WillGibson]

@tcort @smainil @BaseMax I would be interested in your thoughts on this.

I would image adding some information about using mutation testing and other things to CONTRIBUTING.md before merging.

[WillGibson]

Stryker cannot figure out what to do with this file because it has no extension.

I have moved the contents of this into a src directory to follow a more conventional file structure and allow for breaking things into smaller bites along the lines of the single responsibility principal.

[WillGibson]

Assuming we are happy with the initial file re-org, I might move that out to a separate pull request that the resulting commits when we squash and merge cover one concern each.

[WillGibson]

Another reason for having the file extension mentioned in #415.

[WillGibson]

I think this is correct 🤷

[WillGibson]

@tcort @smainil @BaseMax It would be good to get some other brains/eyes on this.

index.js (moved in this pull request to src/index.js) seems to contain things used in src/markdown-link-check.js and should not be used directly.

I think this change is correct, but maybe there is something I'm missing?

[smainil]

@WillGibson great job. Looks good to me.

In addition to unit test and coverage, I think we need to be able to run integration test invoking the check through command line, docker or directly from a nodejs source code

PS: sorry if my english is not as good as yours. It's not my native language

[WillGibson]

In addition to unit test and coverage, I think we need to be able to run integration test invoking the check through command line, docker or directly from a nodejs source code

Good idea. Something like this in a GitHub, but against a file we expect to have only alive links?

./markdown-link-check --verbose --progress test/hash-links.md

That would check it all hooks up correctly and we can leave the detail to the unit tests.

Anything other than a zero exit code would be a fail.

I'll knock up a pull request now...

#416

PS: sorry if my english is not as good as yours. It's not my native language

I honestly wouldn't have noticed if you hadn't mentioned it :-)

[github-actions]

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[WillGibson]

@tcort @smainil @BaseMax It would be good to get some other brains/eyes on this.

index.js (moved in this pull request to src/index.js) seems to contain things used in src/markdown-link-check.js and should not be used directly.

I think this change is correct, but maybe there is something I'm missing?

[WillGibson]

The mutation testing could not deal with this file not having a .js extension, so I moved it to src/markdown-link-check.js and this file just executes that code now.

Also removed some unused variables etc. in the new file now that it's being checked by the linter because it has a .js extension.