Merge pull request #99 from wp-cli/fix/improve-php-unit-integration

Author: schlessera

composer.json

@@ -15,15 +15,16 @@
         "php-parallel-lint/php-console-highlighter": "^0.5",
         "php-parallel-lint/php-parallel-lint": "^1",
         "phpcompatibility/php-compatibility": "^9",
-        "phpunit/phpunit": ">=4.8 <7",
+        "phpunit/phpunit": "^5 | ^6 |^7 | ^8 | ^9",
         "wp-cli/config-command": "^1 || ^2",
         "wp-cli/core-command": "^1 || ^2",
         "wp-cli/eval-command": "^1 || ^2",
         "wp-cli/wp-cli": "^2",
         "wp-coding-standards/wpcs": "^2.1"
     },
     "require-dev": {
-        "roave/security-advisories": "dev-master"
+        "roave/security-advisories": "dev-master",
+        "yoast/phpunit-polyfills": "^0.2.0"
     },
     "config": {
         "platform": {