diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index b3b0fe72af7..863277be2a8 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -27,10 +27,10 @@
 			<directory>tests/phpunit/unit</directory>
 		</testsuite>
 		<testsuite name="extensions:unit">
-			<directory>extensions/*/tests/phpunit/unit</directory>
+			<file>tests/phpunit/suites/ExtensionsUnitTestSuite.php</file>
 		</testsuite>
 		<testsuite name="skins:unit">
-			<directory>skins/*/tests/phpunit/unit</directory>
+			<file>tests/phpunit/suites/SkinsUnitTestSuite.php</file>
 		</testsuite>
 		<testsuite name="includes">
 			<directory>tests/phpunit/includes</directory>
diff --git a/tests/phpunit/bootstrap.php b/tests/phpunit/bootstrap.php
index 75b335f4909..129b56588e9 100644
--- a/tests/phpunit/bootstrap.php
+++ b/tests/phpunit/bootstrap.php
@@ -48,24 +48,40 @@ TestSetup::requireOnceInGlobalScope( MW_INSTALL_PATH . "/includes/DevelopmentSet
 
 TestSetup::applyInitialConfig();
 
-// Since we do not load settings, expect to find extensions and skins
-// in their respective default locations.
-$GLOBALS['wgExtensionDirectory'] = MW_INSTALL_PATH . "/extensions";
-$GLOBALS['wgStyleDirectory'] = MW_INSTALL_PATH . "/skins";
+// Shell out to another script that will give us a list of loaded extensions and skins. We need to do that in another
+// process, not in this one, because loading setting files may have non-trivial side effects that could be hard
+// to undo. This sucks, but there doesn't seem to be a way to get a list of extensions and skins without loading
+// all of MediaWiki, which we don't want to do for unit tests.
+// phpcs:ignore MediaWiki.Usage.ForbiddenFunctions.proc_open
+$process = proc_open(
+	__DIR__ . '/getPHPUnitExtensionsAndSkins.php',
+	[
+		0 => [ 'pipe' ,'r' ],
+		1 => [ 'pipe', 'w' ],
+		2 => [ 'pipe', 'w' ]
+	],
+	$pipes
+);
 
-// Populate classes and namespaces from extensions and skins present in filesystem.
-$directoryToJsonMap = [
-	$GLOBALS['wgExtensionDirectory'] => 'extension*.json',
-	$GLOBALS['wgStyleDirectory'] => 'skin*.json'
-];
+$pathsToJsonFilesStr = stream_get_contents( $pipes[1] );
+fclose( $pipes[1] );
+$cmdErr = stream_get_contents( $pipes[2] );
+fclose( $pipes[2] );
+$exitCode = proc_close( $process );
+if ( $exitCode !== 0 ) {
+	echo "Cannot load list of extensions and skins. Output:\n$cmdErr\n";
+	exit( 1 );
+}
+
+$pathsToJsonFiles = explode( "\n", $pathsToJsonFilesStr );
+
+/** @internal For use in ExtensionsUnitTestSuite and SkinsUnitTestSuite only */
+define( 'MW_PHPUNIT_EXTENSIONS_PATHS', array_map( 'dirname', $pathsToJsonFiles ) );
 
 $extensionProcessor = new ExtensionProcessor();
 
-foreach ( $directoryToJsonMap as $directory => $jsonFilePattern ) {
-	foreach ( new GlobIterator( $directory . '/*/' . $jsonFilePattern ) as $iterator ) {
-		$jsonPath = $iterator->getPathname();
-		$extensionProcessor->extractInfoFromFile( $jsonPath );
-	}
+foreach ( $pathsToJsonFiles as $filePath ) {
+	$extensionProcessor->extractInfoFromFile( $filePath );
 }
 
 $autoload = $extensionProcessor->getExtractedAutoloadInfo( true );
diff --git a/tests/phpunit/getPHPUnitExtensionsAndSkins.php b/tests/phpunit/getPHPUnitExtensionsAndSkins.php
new file mode 100755
index 00000000000..ff4c24061bc
--- /dev/null
+++ b/tests/phpunit/getPHPUnitExtensionsAndSkins.php
@@ -0,0 +1,25 @@
+#!/usr/bin/env php
+<?php
+
+/**
+ * WARNING: Hic sunt dracones!
+ *
+ * This script is used in the PHPUnit bootstrap to get a list of extensions and skins to autoload,
+ * without having the bootstrap file itself load any settings. It is a HUGE but unavoidable hack,
+ * if we want to avoid loading settings in unit tests, and at the same time only load the extensions
+ * enabled in LocalSettings.php without triggering any other side effects of Setup.php and the other
+ * files it includes.
+ * One day this may become unnecessary if we enforce YAML settings with a static list of extensions
+ * and skins (https://www.mediawiki.org/wiki/Manual:YAML_settings_file_format).
+ * The script was introduced for T227900, the idea being to have a single config file that can be used
+ * with both unit and integration tests.
+ * @internal This script should only be invoked by bootstrap.php, as part of the PHPUnit bootstrap process
+ */
+
+require_once __DIR__ . '/bootstrap.common.php';
+
+TestSetup::loadSettingsFiles();
+
+$extensionsAndSkins = ExtensionRegistry::getInstance()->getQueue();
+
+echo implode( "\n", array_keys( $extensionsAndSkins ) );
diff --git a/tests/phpunit/suites/ExtensionsUnitTestSuite.php b/tests/phpunit/suites/ExtensionsUnitTestSuite.php
new file mode 100644
index 00000000000..eed59a6746c
--- /dev/null
+++ b/tests/phpunit/suites/ExtensionsUnitTestSuite.php
@@ -0,0 +1,36 @@
+<?php
+
+use PHPUnit\Framework\TestSuite;
+use SebastianBergmann\FileIterator\Facade;
+
+/**
+ * Test suite that runs extensions unit tests (the `extensions:unit` suite).
+ */
+class ExtensionsUnitTestSuite extends TestSuite {
+	public function __construct() {
+		parent::__construct();
+
+		if ( !defined( 'MW_PHPUNIT_EXTENSIONS_PATHS' ) ) {
+			throw new RuntimeException( 'The PHPUnit bootstrap was not loaded' );
+		}
+		$paths = [];
+		foreach ( MW_PHPUNIT_EXTENSIONS_PATHS as $path ) {
+			// Note that we don't load settings, so we expect to find extensions in their
+			// default location
+			// Standardize directory separators for Windows compatibility.
+			if ( str_contains( strtr( $path, '\\', '/' ), '/extensions/' ) ) {
+				$paths[] = "$path/tests/phpunit/unit";
+			}
+		}
+		foreach ( array_unique( $paths ) as $path ) {
+			$suffixes = [ 'Test.php' ];
+			$fileIterator = new Facade();
+			$matchingFiles = $fileIterator->getFilesAsArray( $path, $suffixes );
+			$this->addTestFiles( $matchingFiles );
+		}
+	}
+
+	public static function suite() {
+		return new self;
+	}
+}
diff --git a/tests/phpunit/suites/SkinsUnitTestSuite.php b/tests/phpunit/suites/SkinsUnitTestSuite.php
new file mode 100644
index 00000000000..5e96f954dc5
--- /dev/null
+++ b/tests/phpunit/suites/SkinsUnitTestSuite.php
@@ -0,0 +1,36 @@
+<?php
+
+use PHPUnit\Framework\TestSuite;
+use SebastianBergmann\FileIterator\Facade;
+
+/**
+ * Test suite that runs skins unit tests (the `skins:unit` suite).
+ */
+class SkinsUnitTestSuite extends TestSuite {
+	public function __construct() {
+		parent::__construct();
+
+		if ( !defined( 'MW_PHPUNIT_EXTENSIONS_PATHS' ) ) {
+			throw new RuntimeException( 'The PHPUnit bootstrap was not loaded' );
+		}
+		$paths = [];
+		foreach ( MW_PHPUNIT_EXTENSIONS_PATHS as $path ) {
+			// Note that we don't load settings, so we expect to find skins in their
+			// default location
+			// Standardize directory separators for Windows compatibility.
+			if ( str_contains( strtr( $path, '\\', '/' ), '/skins/' ) ) {
+				$paths[] = "$path/tests/phpunit/unit";
+			}
+		}
+		foreach ( array_unique( $paths ) as $path ) {
+			$suffixes = [ 'Test.php' ];
+			$fileIterator = new Facade();
+			$matchingFiles = $fileIterator->getFilesAsArray( $path, $suffixes );
+			$this->addTestFiles( $matchingFiles );
+		}
+	}
+
+	public static function suite() {
+		return new self;
+	}
+}