Build/Test Tools: Implement use of the void solution.

> PHPUnit 8.0.0 introduced a `void` return type declaration to the "fixture" methods – `setUpBeforeClass()`, `setUp()`, `tearDown()` and `tearDownAfterClass()`. As the `void` return type was not introduced until PHP 7.1, this makes it more difficult to create cross-version compatible tests when using fixtures, due to signature mismatches.
>
> The `Yoast\PHPUnitPolyfills\TestCases\TestCase` overcomes the signature mismatch by having two versions. The correct one will be loaded depending on the PHPUnit version being used.
>
> When using this TestCase, if an individual test, or another TestCase which extends this TestCase, needs to overload any of the "fixture" methods, it should do so by using a snake_case variant of the original fixture method name, i.e. `set_up_before_class()`, `set_up()`, `assert_pre_conditions()`, `assert_post_conditions()`, `tear_down()`, and `tear_down_after_class()`.
>
> The snake_case methods will automatically be called by PHPUnit.
>
> > IMPORTANT: The snake_case methods should not call the PHPUnit parent, i.e. do not use `parent::setUp()` from within an overloaded `set_up()` method. If necessary, DO call `parent::set_up()`.

Reference: https://github.com/Yoast/PHPUnit-Polyfills#testcases

This commit renames all declared fixture methods, and calls to parent versions of those fixture methods, from camelCase to snake_case.

Follow-up to [51559-51567].

Props jrf, hellofromTonya, johnbillion, netweb, dd32, pputzer, SergeyBiryukov.
See #46149.

git-svn-id: https://develop.svn.wordpress.org/trunk@51568 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/user/author.php

@@ -33,8 +33,8 @@ class Tests_User_Author_Template extends WP_UnitTestCase {
 		);
 	}
 
-	function setUp() {
-		parent::setUp();
+	function set_up() {
+		parent::set_up();
 
 		setup_postdata( get_post( self::$post_id ) );
 	}

tests/phpunit/tests/user/capabilities.php

@@ -53,8 +53,8 @@ class Tests_User_Capabilities extends WP_UnitTestCase {
 		);
 	}
 
-	function setUp() {
-		parent::setUp();
+	function set_up() {
+		parent::set_up();
 		// Keep track of users we create.
 		$this->_flush_roles();
 

tests/phpunit/tests/user/countUserPosts.php

@@ -53,8 +53,8 @@ class Tests_User_CountUserPosts extends WP_UnitTestCase {
 		);
 	}
 
-	public function setUp() {
-		parent::setUp();
+	public function set_up() {
+		parent::set_up();
 		register_post_type( 'wptests_pt' );
 	}
 

tests/phpunit/tests/user/multisite.php

@@ -12,16 +12,16 @@ if ( is_multisite() ) :
 	class Tests_Multisite_User extends WP_UnitTestCase {
 		protected $suppress = false;
 
-		function setUp() {
+		function set_up() {
 			global $wpdb;
-			parent::setUp();
+			parent::set_up();
 			$this->suppress = $wpdb->suppress_errors();
 		}
 
-		function tearDown() {
+		function tear_down() {
 			global $wpdb;
 			$wpdb->suppress_errors( $this->suppress );
-			parent::tearDown();
+			parent::tear_down();
 		}
 
 		function test_remove_user_from_blog() {

tests/phpunit/tests/user/session.php

@@ -7,8 +7,8 @@
  */
 class Tests_User_Session extends WP_UnitTestCase {
 
-	function setUp() {
-		parent::setUp();
+	function set_up() {
+		parent::set_up();
 		remove_all_filters( 'session_token_manager' );
 		$user_id       = self::factory()->user->create();
 		$this->manager = WP_Session_Tokens::get_instance( $user_id );

tests/phpunit/tests/user/slashes.php

@@ -14,8 +14,8 @@ class Tests_User_Slashes extends WP_UnitTestCase {
 		self::$user_id   = $factory->user->create();
 	}
 
-	function setUp() {
-		parent::setUp();
+	function set_up() {
+		parent::set_up();
 
 		wp_set_current_user( self::$author_id );
 

tests/phpunit/tests/user/wpSendUserRequest.php

@@ -63,8 +63,8 @@ class Tests_User_WpSendUserRequest extends WP_UnitTestCase {
 	 *
 	 * @since 4.9.9
 	 */
-	public function setUp() {
-		parent::setUp();
+	public function set_up() {
+		parent::set_up();
 
 		set_current_screen( 'dashboard' );
 		reset_phpmailer_instance();
@@ -75,13 +75,13 @@ class Tests_User_WpSendUserRequest extends WP_UnitTestCase {
 	 *
 	 * @since 4.9.9
 	 */
-	public function tearDown() {
+	public function tear_down() {
 		reset_phpmailer_instance();
 
 		unset( $GLOBALS['locale'] );
 
 		restore_previous_locale();
-		parent::tearDown();
+		parent::tear_down();
 	}
 
 	/**