Files/FileList: fix tests to stop interfering with external standards tests

The AddFileTest.php tests introduced an issue that broke the ability to
run sniff tests for external standards using the PHPCS native test
framework.

This problem was happening because `self::initializeConfigAndRuleset()`
was called in a data provider method. Meaning that the `Config` instance
created inside `initializeConfigAndRuleset()` using `ConfigDouble` was
created before `AllSniffs::suite()` had a chance to get the installed
standards from the `CodeSniffer.conf` configuration file.

To fix this problem, I opted to change the test to create an instance of
 the `File` class (which requires an instance of the `Config` class) in
 the test itself instead of doing that in the data provider.

Author: rodrigoprimo

tests/Core/Files/FileList/AddFileTest.php

@@ -47,15 +47,21 @@ protected function initializeFileList()
     /**
      * Test adding a file to the list.
      *
-     * @param string      $fileName   The name of the file to add.
-     * @param object|null $fileObject An optional file object to add instead of creating a new one.
+     * @param string $fileName       The name of the file to add.
+     * @param bool   $passFileObject Whether to pass a File object to addFile() or not.
      *
      * @dataProvider dataAddFile
      *
      * @return void
      */
-    public function testAddFile($fileName, $fileObject=null)
+    public function testAddFile($fileName, $passFileObject=false)
     {
+        $fileObject = null;
+
+        if ($passFileObject === true) {
+            $fileObject = new File($fileName, self::$ruleset, self::$config);
+        }
+
         $this->assertCount(0, $this->fileList);
 
         $this->fileList->addFile($fileName, $fileObject);
@@ -65,7 +71,7 @@ public function testAddFile($fileName, $fileObject=null)
         $this->assertCount(1, $this->fileList, 'File count mismatch');
         $this->assertArrayHasKey($fileName, $fileListArray, 'File not found in list');
 
-        if (isset($fileObject) === true) {
+        if ($fileObject instanceof File) {
             $this->assertSame($fileObject, $fileListArray[$fileName], 'File object mismatch');
         } else {
             $this->assertInstanceOf(
@@ -81,12 +87,10 @@ public function testAddFile($fileName, $fileObject=null)
     /**
      * Data provider for testAddFile.
      *
-     * @return array<string, array<string, string|object>>
+     * @return array<string, array<string, string|bool>>
      */
     public static function dataAddFile()
     {
-        self::initializeConfigAndRuleset();
-
         return [
             'Regular file'                  => [
                 'fileName' => 'test1.php',
@@ -95,8 +99,8 @@ public static function dataAddFile()
                 'fileName' => 'STDIN',
             ],
             'Regular file with file object' => [
-                'fileName'   => 'test1.php',
-                'fileObject' => new File('test1.php', self::$ruleset, self::$config),
+                'fileName'       => 'test1.php',
+                'passFileObject' => true,
             ],
         ];