Tests: Use a consistent way of setting the Administrator role in Ajax tests.

This removes some duplicate code in favor of calling the `WP_Ajax_UnitTestCase::_setRole()` method created specifically for this purpose and used in other tests.

Follow-up to [500/tests], [37288].

Props martin.krcho.
See #56203.

git-svn-id: https://develop.svn.wordpress.org/trunk@53701 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

tests/phpunit/tests/ajax/Attachments.php

@@ -18,16 +18,7 @@ class Tests_Ajax_Attachments extends WP_Ajax_UnitTestCase {
 	 */
 	public function test_wp_ajax_send_attachment_to_editor_should_return_an_image() {
 		// Become an administrator.
-		$post    = $_POST;
-		$user_id = self::factory()->user->create(
-			array(
-				'role'       => 'administrator',
-				'user_login' => 'user_36578_administrator',
-				'user_email' => '[email protected]',
-			)
-		);
-		wp_set_current_user( $user_id );
-		$_POST = array_merge( $_POST, $post );
+		$this->_setRole( 'administrator' );
 
 		$filename = DIR_TESTDATA . '/images/canola.jpg';
 		$contents = file_get_contents( $filename );
@@ -74,16 +65,7 @@ public function test_wp_ajax_send_attachment_to_editor_should_return_a_link() {
 		$this->skipWithMultisite();
 
 		// Become an administrator.
-		$post    = $_POST;
-		$user_id = self::factory()->user->create(
-			array(
-				'role'       => 'administrator',
-				'user_login' => 'user_36578_administrator',
-				'user_email' => '[email protected]',
-			)
-		);
-		wp_set_current_user( $user_id );
-		$_POST = array_merge( $_POST, $post );
+		$this->_setRole( 'administrator' );
 
 		$filename = DIR_TESTDATA . '/formatting/entities.txt';
 		$contents = file_get_contents( $filename );