Add workaround for fatal error in php-code-coverage library

See sebastianbergmann/php-code-coverage#820

src/main/php/unittest/coverage/impl/Coverage9.class.php

@@ -1,5 +1,6 @@
 <?php namespace unittest\coverage\impl;
 
+use PHPUnit\Runner\BaseTestRunner;
 use SebastianBergmann\CodeCoverage\Driver\Selector;
 use SebastianBergmann\CodeCoverage\Report\Clover;
 use SebastianBergmann\CodeCoverage\Report\Html\Facade;
@@ -8,6 +9,24 @@
 class Coverage9 implements Implementation {
   private $filter, $backing;
 
+  static function __static() {
+
+    // Workaround for fatal error in php-code-coverage when PHPUnit is not loaded
+    // See https://github.com/sebastianbergmann/php-code-coverage/issues/820
+    if (!class_exists(BaseTestRunner::class)) {
+      eval('namespace PHPUnit\Runner; class BaseTestRunner {
+        const STATUS_UNKNOWN    = -1;
+        const STATUS_PASSED     = 0;
+        const STATUS_SKIPPED    = 1;
+        const STATUS_INCOMPLETE = 2;
+        const STATUS_FAILURE    = 3;
+        const STATUS_ERROR      = 4;
+        const STATUS_RISKY      = 5;
+        const STATUS_WARNING    = 6;
+      }');
+    }
+  }
+
   /** Creates a new coverage implementation for php-code-coverage >= 9.0 */
   public function __construct() {
     $this->filter= new Filter();