Update unit tests for compatibility with PHPUnit 7.5.

[briandotdev]

Summary

I understand that this cannot be merged as is because of the integration tests but hopefully it's useful as a starting point for upgrading to PHPUnit 7 which is required for PHP 7.3 compatibility.

• Update Composer version requirements.
• Update phpunit.xml to remove obsolete syntaxCheck and enable console colors.
• Replace references to PHPUnit_Framework_TestCase with PHPUnit\Framework\TestCase.
• Moved test setup routines from _construct() to setUp().
• Replaced depreciated @expectedException and setExpectedException() with expectException().
• Added assertNull() to seven test routines that did not return a response or assert any tests.
• Added test for expected HTTP response code to HTTP test that did not make any assertions.

[crookedneighbor]

Thanks for all the work you did on this. We're doing internal testing and finishing up the integration tests now.

[crookedneighbor]

We incorporated these changes as part of v4.0.0, thanks for all your work on this!

[briandotdev]

👍Use the service a ton and happy to help.