test(sample-14): added unit test and other improvements

[Tony133]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

Issue Number: #1539

What is the new behavior?

Added unit tests in sample sample-14-mongoose-base and other improvements.

Does this PR introduce a breaking change?

• Yes
• No

Other information

This PR, added unit tests in sample sample-14-mongoose-base and other improvements.

[Tony133]

PR to evaluate 👀 🤞😻

[coveralls]

Pull Request Test Coverage Report for Build ba3acf56-db4e-4ab0-a906-3414061031c1

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.174%

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Totals
Change from base Build 8bef8cae-6c99-4a3b-8be5-5ff1febbdda7:	0.0%
Covered Lines:	5658
Relevant Lines:	6008

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💛 - Coveralls

[kamilmysliwiec]

LGTM