Abstract tests do not need coverage data

Coverage data for abstract classes is optional. In most cases it will
make sense to belong to the concrete class that implements it.

moodle/Sniffs/PHPUnit/TestCaseCoversSniff.php

@@ -22,6 +22,7 @@
 use PHP_CodeSniffer\Sniffs\Sniff;
 use PHP_CodeSniffer\Files\File;
 use PHP_CodeSniffer\Util\Tokens;
+use PHPCSUtils\Utils\ObjectDeclarations;
 
 /**
  * Checks that a test file has the @coversxxx annotations properly defined.
@@ -46,7 +47,6 @@ public function register() {
      * @param int $pointer The position in the stack.
      */
     public function process(File $file, $pointer) {
-
         // Before starting any check, let's look for various things.
 
         // If we aren't checking Moodle 4.0dev (400) and up, nothing to check.
@@ -78,6 +78,12 @@ public function process(File $file, $pointer) {
         // Iterate over all the classes (hopefully only one, but that's not this sniff problem).
         $cStart = $pointer;
         while ($cStart = $file->findNext(T_CLASS, $cStart + 1)) {
+            $classInfo = ObjectDeclarations::getClassProperties($file, $cStart);
+            if ($classInfo['is_abstract']) {
+                // Abstract classes are not tested.
+                // Coverage information belongs to the concrete classes that extend them.
+                continue;
+            }
             $class = $file->getDeclarationName($cStart);
             $classCovers = false; // To control when the class has a @covers tag.
             $classCoversNothing = false; // To control when the class has a @coversNothing tag.