Use fs.FS abstraction for filesystem

[tigh-latte]

🤔 What's changed?

Allow users to supply a fs.FS to files from. If not provided, we will fallback to the standard os file operations.

⚡️ What's your motivation?

As fs.FS is an interface it gives users flexibility beyond just the operating system's filesystem, such as mocking (see, for example, the tests. We no longer write data to /tmp) or at the very least, an in-memory fs. But the key feature is that it allows us to compile the feature files into an executable test binary, allowing that binary to be shipped independent from the feature files.

//go:embed features/*
var featuresData embed.FS

...

var opts = godog.Options{
	Paths: []string{"features"},
	FS:    featureData,
}

Then we can just:

> go test -c ./test/integration/integration_test.go
> mv integration.test /some/random/dir
> cd /some/random/dir
> ./integration.test

Currently I embed all test data into my test suite, and sometimes deploy these tests into a restricted environment for some non-user facing service tests in a live environment. With the current set up of godog, I have to also be concerned with shipping the feature files and placing them the correct location on the filesystem. This change would let users just fire a test binary into a scratch container and run without being concerned the underlying filesystem.

🏷️ What kind of change is this?

• 🏦 Refactoring/debt/DX (improvement to code design, tooling, documentation etc. without changing behaviour)
• ⚡ New feature (non-breaking change which adds new behaviour)

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

---

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[vearutop]

This is a great feature, thank you!

I'm a bit concerned with the necessity of manual upgrade of existing code, as in

var opts = godog.Options{
	Paths: []string{"../testfiles/features"},
}

becomes

var opts = godog.Options{
	Paths: []string{"testfiles/features"},
	FS:    os.DirFS("../"),
}

It seems we can preserve backwards compatibility by having a special case for nil opts.FS, so that Paths are processed as before, what do you think?

[tigh-latte]

Sure we can do that, I'll see to sorting this at some point today.

[tigh-latte]

That's done here @vearutop

[tigh-latte]

@vearutop I fixed the build here, sorry about that.

# tigh in ~/go/src/github.com/tigh-latte/godog on git:enhancement/fs o
> go test ./...
ok      github.com/cucumber/godog       0.362s
?       github.com/cucumber/godog/cmd/godog     [no test files]
?       github.com/cucumber/godog/cmd/godog/internal    [no test files]
?       github.com/cucumber/godog/colors        [no test files]
ok      github.com/cucumber/godog/formatters    0.006s
ok      github.com/cucumber/godog/internal/builder      5.355s
ok      github.com/cucumber/godog/internal/flags        0.002s
ok      github.com/cucumber/godog/internal/formatters   0.026s
ok      github.com/cucumber/godog/internal/models       0.006s
ok      github.com/cucumber/godog/internal/parser       0.003s
ok      github.com/cucumber/godog/internal/storage      0.004s
ok      github.com/cucumber/godog/internal/tags 0.002s
?       github.com/cucumber/godog/internal/testutils    [no test files]
?       github.com/cucumber/godog/internal/utils        [no test files]

[codecov]

Codecov Report

Merging #550 (f9d3db5) into main (3bd9e9c) will increase coverage by 0.69%.
The diff coverage is 84.78%.

@@            Coverage Diff             @@
##             main     #550      +/-   ##
==========================================
+ Coverage   82.24%   82.94%   +0.69%     
==========================================
  Files          27       28       +1     
  Lines        3340     3371      +31     
==========================================
+ Hits         2747     2796      +49     
+ Misses        484      461      -23     
- Partials      109      114       +5     

Impacted Files	Coverage Δ
run.go	77.13% <69.56%> (+2.65%)	⬆️
internal/parser/parser.go	77.50% <100.00%> (+11.48%)	⬆️
internal/storage/fs.go	100.00% <100.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[tigh-latte]

@vearutop Ok I've added tests to cover the new storage.FS wrapper, and used fstest.MapFS to mock some file system failures to increase coverage in certain areas. Hopefully Codecov will be happy now.

[aslakhellesoy]

Hi @tigh-latte,

Thanks for your making your first contribution to Cucumber, and welcome to the Cucumber committers team! You can now push directly to this repo and all other repos under the cucumber organization! 🍾

In return for this generous offer we hope you will:

• ✅ Continue to use branches and pull requests. When someone on the core team approves a pull request (yours or someone else's), you're welcome to merge it yourself.
• 💚 Commit to setting a good example by following and upholding our code of conduct in your interactions with other collaborators and users.
• 💬 Join the community Slack channel to meet the rest of the team and make yourself at home.
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On behalf of the Cucumber core team,
Aslak Hellesøy
Creator of Cucumber