Clean up XUnitParser and add tests.

[ericsnowcurrently]

This is a precursor to the fix for (for #6990).

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• [ ] Has a news entry file (remember to thank yourself!)
• Appropriate comments and documentation strings in the code
• [ ] Has sufficient logging.
• [ ] Has telemetry for enhancements.
• Unit tests & system/integration tests are added/updated
• [ ] Test plan is updated as appropriate
• [ ] package-lock.json has been regenerated by running npm install (if dependencies have changed)
• [ ] The wiki is updated with any design decisions/details.

[codecov-io]

Codecov Report

Merging #7263 into master will increase coverage by 0.87%.
The diff coverage is 71.09%.

@@            Coverage Diff             @@
##           master    #7263      +/-   ##
==========================================
+ Coverage   57.82%   58.69%   +0.87%     
==========================================
  Files         494      494              
  Lines       21475    21825     +350     
  Branches     3494     3498       +4     
==========================================
+ Hits        12417    12811     +394     
+ Misses       8267     8217      -50     
- Partials      791      797       +6

Impacted Files	Coverage Δ
src/client/testing/types.ts	95% <100%> (+0.88%)	⬆️
src/client/testing/explorer/failedTestHandler.ts	95.83% <100%> (+0.18%)	⬆️
...ient/testing/common/services/testResultsService.ts	88% <100%> (+0.24%)	⬆️
...rc/client/testing/explorer/testTreeViewProvider.ts	66.21% <100%> (ø)	⬆️
src/client/testing/common/types.ts	100% <100%> (ø)	⬆️
...nt/testing/common/services/discoveredTestParser.ts	16.1% <22.22%> (ø)	⬆️
src/client/testing/nosetest/runner.ts	18.86% <50%> (ø)	⬆️
src/client/testing/pytest/runner.ts	18% <50%> (ø)	⬆️
src/client/testing/common/xUnitParser.ts	66.1% <62.26%> (+58.52%)	⬆️
src/client/testing/explorer/commandHandlers.ts	77.27% <66.66%> (-0.51%)	⬇️
... and 37 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b4aa1f0...2d46d6a. Read the comment docs.

[kimadeline]

Can you rename helpers-declarative, helpers-nodes and helpers-results using camelCase? I'm also not sold on the idea of splitting the helpers in 4 different files 🤔 The unit test imports

import { createResults } from '../helpers-declarative';
import { TestItem } from '../helpers-nodes';
import { createEmptyResults } from '../helpers-results';

so why not have all these methods (and the rest of the the helper methods) in the same spot?

[ericsnowcurrently]

As to the multiple "helpers-" files, there are several reasons:

• there is a natural division between the different modules
• as a single file it would be much longer than I like to make files (<300 lines)
• the structure is a nudge toward changes we should make in src/client/testing/common/types.ts
• I almost made a "helpers" subpackage but chickened out :)

[kimadeline]

Once you update how you structure your helpers-* files we good to go 👍