Feat(test): giving some love to tests

[rgoupil]

Description

It's quite common to look at tests when docs are not enough, especially for specific use case.
In its current state, the code is not showing using the framework in the most elegant way and we still have a few URL dependencies.
This PR aim to improve all those points by giving some love to the tests <3

It also introduce a single breaking change which is to change the default value for the port parameter of DanetApplication.listen() from 3000 to 0. Most respectable frameworks (Express, NestJS, Oak, etc.) will use 0 if no port is provided, why not Danet!

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Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

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Checklist:

• I have run deno lint AND deno fmt AND deno task test and got no errors.
• I have followed the contributing guidelines of this project as mentioned in CONTRIBUTING.md
• I have checked to ensure there aren't other open Pull Requests for the same update/change?
• I have performed a self-review of my own code
• I have made corresponding changes needed to the documentation

[Sorikairox]

Nice PR ! Not quite sure about the random port, so it would be cool to put it back to a fixed number (maybe not 3000, but 4242 or idk)

[codecov-commenter]

Codecov Report

Merging #47 (a49eb99) into main (123e508) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #47   +/-   ##
=======================================
  Coverage   84.60%   84.60%           
=======================================
  Files          26       26           
  Lines        1104     1104           
  Branches       90       90           
=======================================
  Hits          934      934           
  Misses        168      168           
  Partials        2        2           

Impacted Files	Coverage Δ
src/deps.ts	100.00% <ø> (ø)

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