Duplicate code is one of the most pungent code smells. A rule that is often used is to re-structure code once it is duplicated in three or more places.
Common duplication problems, and corresponding solutions are:
| 1 | <?php  | 
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| 20 | class Test_Admin_Menu extends WP_UnitTestCase { | 
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| 21 | |||
| 22 | /**  | 
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| 23 | * Menu data fixture.  | 
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| 24 | *  | 
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| 25 | * @var array  | 
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| 26 | */  | 
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| 27 | public static $menu_data;  | 
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| 28 | |||
| 29 | /**  | 
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| 30 | * Submenu data fixture.  | 
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| 31 | *  | 
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| 32 | * @var array  | 
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| 33 | */  | 
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| 34 | public static $submenu_data;  | 
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| 35 | |||
| 36 | /**  | 
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| 37 | * Test domain.  | 
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| 38 | *  | 
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| 39 | * @var string  | 
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| 40 | */  | 
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| 41 | public static $domain;  | 
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| 42 | |||
| 43 | /**  | 
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| 44 | * Admin menu instance.  | 
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| 45 | *  | 
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| 46 | * @var Admin_Menu  | 
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| 47 | */  | 
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| 48 | public static $admin_menu;  | 
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| 49 | |||
| 50 | /**  | 
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| 51 | * Mock user ID.  | 
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| 52 | *  | 
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| 53 | * @var int  | 
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| 54 | */  | 
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| 55 | private static $user_id = 0;  | 
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| 56 | |||
| 57 | /**  | 
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| 58 | * Create shared fixtures.  | 
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| 59 | *  | 
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| 60 | * @param WP_UnitTest_Factory $factory Fixture factory.  | 
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| 61 | */  | 
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| 62 | View Code Duplication | 	public static function wpSetUpBeforeClass( $factory ) { | 
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| 63 | static::$domain = ( new Status() )->get_site_suffix();  | 
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| 64 | static::$user_id = $factory->user->create( array( 'role' => 'administrator' ) );  | 
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                         | 
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| 65 | static::$menu_data = get_menu_fixture();  | 
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| 66 | static::$submenu_data = get_submenu_fixture();  | 
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| 67 | }  | 
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| 68 | |||
| 69 | /**  | 
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| 70 | * Set up data.  | 
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| 71 | */  | 
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| 72 | View Code Duplication | 	public function setUp() { | 
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| 84 | |||
| 85 | /**  | 
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| 86 | * Test_Admin_Menu.  | 
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| 87 | *  | 
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| 88 | * @covers ::reregister_menu_items  | 
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| 89 | */  | 
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| 90 | 	public function test_admin_menu_output() { | 
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| 103 | |||
| 104 | /**  | 
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| 105 | * Shim wpcomsh fallback site icon.  | 
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| 106 | *  | 
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| 107 | * @return string  | 
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| 108 | */  | 
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| 109 | 	public function wpcomsh_site_icon_url() { | 
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| 112 | |||
| 113 | /**  | 
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| 114 | * Custom site icon.  | 
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| 115 | *  | 
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| 116 | * @return string  | 
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| 117 | */  | 
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| 118 | 	public function custom_site_icon_url() { | 
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| 121 | |||
| 122 | /**  | 
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| 123 | * Tests add_my_home_menu  | 
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| 124 | *  | 
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| 125 | * @covers ::add_my_home_menu  | 
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| 126 | */  | 
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| 127 | 	public function test_add_my_home_menu() { | 
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| 149 | |||
| 150 | /**  | 
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| 151 | * Tests add_stats_menu  | 
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| 152 | *  | 
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| 153 | * @covers ::add_stats_menu  | 
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| 154 | */  | 
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| 155 | 	public function test_add_stats_menu() { | 
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| 156 | global $menu;  | 
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| 157 | |||
| 158 | static::$admin_menu->add_stats_menu();  | 
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| 159 | |||
| 160 | $this->assertSame( 'https://wordpress.com/stats/day/' . static::$domain, $menu['3.86682'][2] );  | 
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| 161 | }  | 
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| 162 | |||
| 163 | /**  | 
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| 164 | * Tests add_upgrades_menu  | 
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| 165 | *  | 
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| 166 | * @covers ::add_upgrades_menu  | 
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| 167 | */  | 
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| 168 | View Code Duplication | 	public function test_add_upgrades_menu() { | 
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| 176 | |||
| 177 | /**  | 
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| 178 | * Tests add_posts_menu  | 
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| 179 | *  | 
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| 180 | * @covers ::add_posts_menu  | 
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| 181 | */  | 
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| 182 | View Code Duplication | 	public function test_add_posts_menu() { | 
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| 190 | |||
| 191 | /**  | 
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| 192 | * Tests add_media_menu  | 
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| 193 | *  | 
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| 194 | * @covers ::add_media_menu  | 
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| 195 | */  | 
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| 196 | View Code Duplication | 	public function test_add_media_menu() { | 
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| 204 | |||
| 205 | /**  | 
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| 206 | * Tests add_page_menu  | 
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| 207 | *  | 
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| 208 | * @covers ::add_page_menu  | 
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| 209 | */  | 
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| 210 | View Code Duplication | 	public function test_add_page_menu() { | 
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| 218 | |||
| 219 | /**  | 
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| 220 | * Tests add_custom_post_type_menu  | 
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| 221 | *  | 
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| 222 | * @covers ::add_custom_post_type_menu  | 
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| 223 | */  | 
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| 224 | 	public function test_add_custom_post_type_menu() { | 
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| 251 | |||
| 252 | /**  | 
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| 253 | * Tests add_comments_menu  | 
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| 254 | *  | 
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| 255 | * @covers ::add_comments_menu  | 
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| 256 | */  | 
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| 257 | View Code Duplication | 	public function test_add_comments_menu() { | 
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| 265 | |||
| 266 | /**  | 
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| 267 | * Tests add_appearance_menu  | 
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| 268 | *  | 
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| 269 | * @covers ::add_appearance_menu  | 
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| 270 | */  | 
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| 271 | 	public function test_add_appearance_menu() { | 
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| 281 | |||
| 282 | /**  | 
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| 283 | * Tests add_plugins_menu  | 
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| 284 | *  | 
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| 285 | * @covers ::add_plugins_menu  | 
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| 286 | */  | 
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| 287 | 	public function test_add_plugins_menu() { | 
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| 303 | |||
| 304 | /**  | 
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| 305 | * Tests add_users_menu  | 
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| 306 | *  | 
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| 307 | * @covers ::add_users_menu  | 
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| 308 | */  | 
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| 309 | 	public function test_add_users_menu() { | 
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| 350 | |||
| 351 | /**  | 
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| 352 | * Tests add_tools_menu  | 
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| 353 | *  | 
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| 354 | * @covers ::add_tools_menu  | 
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| 355 | */  | 
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| 356 | 	public function test_add_tools_menu() { | 
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| 366 | |||
| 367 | /**  | 
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| 368 | * Tests add_options_menu  | 
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| 369 | *  | 
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| 370 | * @covers ::add_options_menu  | 
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| 371 | */  | 
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| 372 | View Code Duplication | 	public function test_add_options_menu() { | 
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| 379 | |||
| 380 | /**  | 
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| 381 | * Tests add_jetpack_menu  | 
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| 382 | *  | 
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| 383 | * @covers ::add_jetpack_menu  | 
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| 384 | */  | 
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| 385 | 	public function test_add_jetpack_menu() { | 
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| 394 | |||
| 395 | /**  | 
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| 396 | * Tests add_gutenberg_menus  | 
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| 397 | *  | 
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| 398 | * @covers ::add_gutenberg_menus  | 
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| 399 | */  | 
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| 400 | 	public function test_add_gutenberg_menus() { | 
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| 420 | }  | 
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| 421 | 
Let’s assume you have a class which uses late-static binding:
The code above will run fine in your PHP runtime. However, if you now create a sub-class and call the
getSomeVariable()on that sub-class, you will receive a runtime error:In the case above, it makes sense to update
SomeClassto useselfinstead: