test(sample-12): added unit and e2e tests

[pacyL2K19]

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: Added unit and e2e tests to the sample-12

What is the current behavior?

Issue Number: #1539

What is the new behavior?

Does this PR introduce a breaking change?

• Yes
• No

Other information

I have added unit and e2e tests to the sample-12-graphql-schema-first
Increased the test coverage
This is my first contribution to the project, I may miss a couple of things, I will appreciate any feedback

[coveralls]

Pull Request Test Coverage Report for Build 80567a20-17a5-4037-8fd1-f2a66e07e4f6

• 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 92.258%

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Totals
Change from base Build 07271e8a-a67e-47df-be5c-241b54a18b75:	0.0%
Covered Lines:	6697
Relevant Lines:	7259

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💛 - Coveralls

[pacyL2K19]

@micalevisk fixed the conflicts by rebasing with nest:master, please have a look