Update for modern PHPUnit

[orlitzky]

PHPUnit is up to version 9.x now, and the test suite stops working somewhere around 6.x. The first, big problem is that they refactored the names,

• PHPUnit_Framework_TestCase -> PHPUnit\Framework\TestCase
• PHPUnit_Framework_TestSuite -> PHPUnit\Framework\TestSuite

Then there are some minor things, like the assertEquals method will no longer accept a null for the string. Finally, in the latest versions of PHPUnit, a few functions were removed/renamed:

• assertAttributeSame() is deprecated and will be removed in PHPUnit 9.
• readAttribute() is deprecated and will be removed in PHPUnit 9.
• getObjectAttribute() is deprecated and will be removed in PHPUnit 9.
• The optional $delta parameter of assertEquals() is deprecated and will be removed in PHPUnit 9. Refactor your test to use assertEqualsWithDelta() instead.