adds phpunit as dev dependency

[Headd2k]

this pr adds missing phpunit dev dependencies, fixes existing tests and sets base php platform in composer to ensure only compatible dependencies

Q	A
Bug fix?	no
New feature?	no
BC breaks?	no
Deprecations?	no
Related tickets	fix #182
Documentation	-
License	MIT

What's in this PR?

• adds required dev dependencies to composer.json to run existing phpunit tests
• fixes existing phpunit tests
• adds phpunit execution to composer test scripts
• adds base platform to composer.json to ensure only php 7.1 compatible dependencies getting added

Why?

Existing PHPUnit tests should get executed during CI runs.

Checklist

• Updated CHANGELOG.md to describe BC breaks / deprecations | new feature | bugfix (@dbu thinks: not needed for a testing setup change)

To Do

• Need feedback if we could/should replace nyholm/psr7 dependencies/usage in tests with something else
• Need feedback if setting the base platform in composer.json to ensure php 7.1 compatible dependencies only is okay

[dbu]

oh, i was not aware that we also have phpunit tests in here... thanks for spotting and cleaning it all up.

i only have one small question what the platform => php config option is for?

[dbu]

sorry, reading the questions now:

• i would leave the platform thingy out. on travis-ci we do run with all minor php versions we support, that should cover this.
• nyholm/psr7 seems fine to me

[Headd2k]

thanks for your quick reply! i updated the pr to remove the base php platform setting. the initial purpose was to have a "safer" process for adding new dependencies. i currently have php 7.2 on my local machine. when i check out the library and run "composer require --dev phpunit/phpunit" i get phpunit 8.x installed because this version is compatible with php 7.2. but the library must support php 7.1. so with the "platform" setting in the composer configuration the require command would have installed phpunit 7.x as this was the last phpunit version branch supporting php 7.1.

[dbu]

thanks for the explanation. i don't think we need to worry about adding dependencies: travis-ci will catch it if it goes wrong, and its not often that we add new dependencies. (a library is much more stable than an application usually)