simplify tests

[IonBazan]

What is the reason for this PR?

This PR removes a lot of duplicated code and refactors all the tests. This replaces the previous PR without style changes (sorry for that) #90.

Summary of changes

• Initializing Generator instance for each test in setUp method
• Sets the seed to 1 to make results predictable
• Adding protected function getProviders(): iterable allowing developers to easily specify providers needed in the test
• Migrated most of $this->assert* and $this->fail() to static calls
• Uses dedicated assertNotContains or assertGreaterThan assertions instead of asserting that comparison returns false

Review checklist

• All checks have passed
• Changes are approved by maintainer

[mfn]

Migrated most of $this->assert* and $this->fail() to static calls

This should be enforced via the style checker so no manual work and future contributions automatically adhere to the same style, see #90 (comment)

[IonBazan]

@mfn Unfortunately, StyleCI does not support php_unit_test_case_static_method_calls fixer: https://github.styleci.io/analyses/Yjmr4G

[GrahamCampbell]

StyleCI will do soon. :)

[bram-pkg]

Can this be merged? @GrahamCampbell