docs: update unit-testing recipe

[arturovt]

In this commit, we updated the unit-testing recipe with a lot more useful information and code guides. We included the actions collector snippet, which has been successfully used in production apps for years and can be safely applied to external user apps.

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[bundlemon[bot]]

BundleMon (Integration Projects)

Unchanged files (2)

Status | Path | Size | Limits :------------: | ------------ | :------------: | :------------: :white_check_mark: | Main bundles(Gzip)
_{hello-world-ng17/dist-integration/main.(hash)
.js}
| 68.53KB | +1% :white_check_mark: | Main bundles(Gzip)
_{hello-world-ng16/dist-integration/main.(hash)
.js}
| 67.54KB | +1%

No change in files bundle size

Final result: :white_check_mark:

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Current branch size history | Target branch size history

[codeclimate[bot]]

Code Climate has analyzed commit 84743e88 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 95.5% (0.0% change).

View more on Code Climate.