Prevent cache gc from happening during test suite runs, and add output so it is clear why it is blocking for a bit

phpunit.xml.dist

@@ -16,6 +16,7 @@
 >
     <php>
         <env name="SYMFONY_DEPRECATIONS_HELPER" value="weak"/>
+        <env name="COMPOSER_TEST_SUITE" value="1"/>
     </php>
     <testsuites>
         <testsuite name="Composer Test Suite">

src/Composer/Cache.php

@@ -24,7 +24,7 @@ use Symfony\Component\Finder\Finder;
  */
 class Cache
 {
-    private static $cacheCollected = false;
+    private static $cacheCollected = null;
     private $io;
     private $root;
     private $enabled = true;
@@ -191,7 +191,20 @@ class Cache
 
     public function gcIsNecessary()
     {
-        return (!self::$cacheCollected && !mt_rand(0, 50));
+        if (self::$cacheCollected) {
+            return false;
+        }
+
+        self::$cacheCollected = true;
+        if (getenv('COMPOSER_TEST_SUITE')) {
+            return false;
+        }
+
+        if (PHP_VERSION_ID > 70000) {
+            return !random_int(0, 50);
+        }
+
+        return !mt_rand(0, 50);
     }
 
     public function remove($file)

src/Composer/Downloader/FileDownloader.php

@@ -84,6 +84,7 @@ class FileDownloader implements DownloaderInterface, ChangeReportInterface
         $this->filesystem = $filesystem ?: new Filesystem($this->process);
 
         if ($this->cache && $this->cache->gcIsNecessary()) {
+            $this->io->writeError('Running cache garbage collection', true, IOInterface::VERY_VERBOSE);
             $this->cache->gc($config->get('cache-files-ttl'), $config->get('cache-files-maxsize'));
         }
     }