Tests: Add a unit test for PHP 8.1 deprecation notice in wp_user_settings().

This ensures that PHP 8.1 "passing null to non-nullable" deprecation notice is not thrown for the `$domain` parameter of `setcookie()` calls in the function.

Follow-up to [53490].

See #54914.

git-svn-id: https://develop.svn.wordpress.org/trunk@53493 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/option/wpUserSettings.php

@@ -0,0 +1,36 @@
+<?php
+/**
+ * Test wp_user_settings().
+ *
+ * @group option
+ * @group user
+ * @covers ::wp_user_settings
+ */
+class Tests_Option_wpUserSettings extends WP_UnitTestCase {
+
+	/**
+	 * Tests that PHP 8.1 "passing null to non-nullable" deprecation notice
+	 * is not thrown for the `$domain` parameter of setcookie() calls in the function.
+	 *
+	 * The notice that we should not see:
+	 * `Deprecated: setcookie(): Passing null to parameter #5 ($domain) of type string is deprecated`.
+	 *
+	 * Note: This does not test the actual functioning of wp_user_settings().
+	 * It just and only tests for/against the deprecation notice.
+	 *
+	 * @ticket 54914
+	 */
+	public function test_wp_user_settings_does_not_throw_deprecation_notice_for_setcookie() {
+		set_current_screen( 'edit.php' );
+		wp_set_current_user( self::factory()->user->create() );
+
+		// Verify that the function's starting conditions are satisfied.
+		$this->assertTrue( is_admin() );
+		$this->assertGreaterThan( 0, get_current_user_id() );
+
+		// `Cannot modify header information - headers already sent by...` from setcookie().
+		$this->expectWarning();
+
+		wp_user_settings();
+	}
+}