Fails with PHPUnit 6.0.6

[ChrisWiegman]

Using the latest PHPUnit WP_Mock causes a failure with the following error:

PHP Fatal error: Class 'PHPUnit_Framework_TestCase' not found in .../vendor/10up/wp_mock/WP_Mock/Tools/TestCase.php on line 12

[johnpbloch]

It looks like PHPUnit 6.0 changed PHPUnit_Framework_TestCase to PHPUnit\Framework\TestCase. For now, I think we should modify the composer requirements from "phpunit/phpunit": ">=4.3" to "phpunit/phpunit": ">=4.3 <6.0" in the dev branch and "phpunit/phpunit": ">=3.7 <6.0" in master. We can look into how we might accommodate both paradigms later, but for now, let's just make sure composer lets users know about the incompatibility. What do you think @ChrisWiegman ?

[johnpbloch]

The other option would be to specify phpunit >= 6.0 as conflicting with wp mock

[ChrisWiegman]

Either would handle it for now, at least in preventing issues that is. I'd like to keep this issue open past the version limitation however in an effort to put in place a more permanent fix later.