diff --git a/.github/workflows/build-test-measure.yml b/.github/workflows/build-test-measure.yml
index 285822326fd..b55afa81a4e 100644
--- a/.github/workflows/build-test-measure.yml
+++ b/.github/workflows/build-test-measure.yml
@@ -71,11 +71,11 @@ jobs:
           echo "Changed JS file count: $JS_FILE_COUNT"
           echo "Changed GHA workflow file count: $GHA_WORKFLOW_COUNT"
 
-          echo "::set-output name=count::$FILE_COUNT"
-          echo "::set-output name=php-count::$PHP_FILE_COUNT"
-          echo "::set-output name=css-count::$CSS_FILE_COUNT"
-          echo "::set-output name=js-count::$JS_FILE_COUNT"
-          echo "::set-output name=gha-workflow-count::$GHA_WORKFLOW_COUNT"
+          echo "count=$FILE_COUNT" >> $GITHUB_OUTPUT
+          echo "php-count=$PHP_FILE_COUNT" >> $GITHUB_OUTPUT
+          echo "css-count=$CSS_FILE_COUNT" >> $GITHUB_OUTPUT
+          echo "js-count=$JS_FILE_COUNT" >> $GITHUB_OUTPUT
+          echo "gha-workflow-count=$GHA_WORKFLOW_COUNT" >> $GITHUB_OUTPUT
         env:
           # Ignore Paths:
           # - .github/
@@ -176,7 +176,7 @@ jobs:
 
       - name: Get Composer Cache Directory
         id: composer-cache
-        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+        run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
 
       - name: Configure Composer cache
         uses: actions/cache@v3.0.11
@@ -222,7 +222,7 @@ jobs:
 
       - name: Get Composer Cache Directory
         id: composer-cache
-        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+        run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
 
       - name: Configure Composer cache
         uses: actions/cache@v3.0.11
@@ -304,7 +304,7 @@ jobs:
 
       - name: Get Composer Cache Directory
         id: composer-cache
-        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+        run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
 
       - name: Configure Composer cache
         uses: actions/cache@v3.0.11
@@ -457,7 +457,7 @@ jobs:
       - name: Get Composer Cache Directory
         if: needs.pre-run.outputs.changed-php-count > 0
         id: composer-cache
-        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+        run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
 
       - name: Configure Composer cache
         if: needs.pre-run.outputs.changed-php-count > 0
@@ -475,7 +475,7 @@ jobs:
           composer remove --dev phpdocumentor/reflection
           composer install --prefer-dist --ignore-platform-reqs --no-progress --no-interaction
 
-    # See https://github.com/wp-cli/wp-cli/issues/5484
+      # See https://github.com/wp-cli/wp-cli/issues/5484
       - name: Remove conflicting Requests library
         if: needs.pre-run.outputs.changed-php-count > 0
         run: composer remove --dev --ignore-platform-reqs --no-interaction --no-scripts  roave/security-advisories wp-cli/export-command wp-cli/extension-command wp-cli/wp-cli wp-cli/wp-cli-tests
@@ -567,7 +567,76 @@ jobs:
           flags: php,unit
           fail_ci_if_error: true
 
-  #-----------------------------------------------------------------------------------------------------------------------
+#-----------------------------------------------------------------------------------------------------------------------
+
+  unit-test-multisite-php:
+    name: 'Unit Tests Multisite: PHP 7.4, WP Latest'
+    needs: pre-run
+    runs-on: ubuntu-latest
+    if: needs.pre-run.outputs.changed-php-count > 0
+    strategy:
+      matrix:
+        testsuite: ['default', 'external-http']
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Setup Node
+        uses: actions/setup-node@v3.5.1
+        with:
+          node-version-file: '.nvmrc'
+          cache: npm
+
+      - name: Get Composer Cache Directory
+        id: composer-cache
+        run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
+
+      - name: Configure Composer cache
+        uses: actions/cache@v3.0.11
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-composer-
+
+      - name: Install Node dependencies
+        run: npm ci
+        env:
+          CI: true
+
+      - name: Install Composer dependencies
+        run: |
+          # phpdocumentor/reflection has to be removed as it makes use of an outdated dependency.
+          composer remove --dev phpdocumentor/reflection
+          composer install --prefer-dist --ignore-platform-reqs --no-progress --no-interaction
+
+      # See https://github.com/wp-cli/wp-cli/issues/5484
+      - name: Remove conflicting Requests library
+        run: composer remove --dev --ignore-platform-reqs --no-interaction --no-scripts  roave/security-advisories wp-cli/export-command wp-cli/extension-command wp-cli/wp-cli wp-cli/wp-cli-tests
+
+      - name: Update PHPUnit
+        if: needs.pre-run.outputs.changed-php-count > 0
+        run: |
+          # We are using PHP 7.4 and WP Latest.
+          echo "Installing latest version of PHPUnit"
+          composer update --ignore-platform-reqs --no-interaction --no-scripts yoast/phpunit-polyfills --with-dependencies
+
+      - name: Build plugin
+        run: npm run build:js
+
+      - name: Move amp-wp to amp
+        run: cp -r "$PWD" "/tmp/amp"
+
+      - name: Start wp-env
+        working-directory: /tmp/amp
+        run: npm run wp-env start
+
+      - name: Run multisite unit tests
+        working-directory: /tmp/amp
+        run: npm run test:php:multisite ${{ matrix.testsuite == 'external-http' && '-- --testsuite external-http' || '' }}
+
+#-----------------------------------------------------------------------------------------------------------------------
 
   feature-test-php:
     name: "Feature test${{ matrix.coverage && ' (with coverage)' || '' }}: PHP ${{ matrix.php }}, WP ${{ matrix.wp }}"
@@ -641,7 +710,7 @@ jobs:
 
       - name: Get Composer Cache Directory
         id: composer-cache
-        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+        run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
 
       - name: Configure Composer cache
         uses: actions/cache@v3.0.11
@@ -741,8 +810,7 @@ jobs:
 
       - name: Get Composer Cache Directory
         id: composer-cache
-        run: |
-          echo "::set-output name=dir::$(composer config cache-files-dir)"
+        run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
 
       - name: Configure Composer cache
         uses: actions/cache@v3.0.11
@@ -774,11 +842,11 @@ jobs:
 
       - name: Retrieve branch name
         id: retrieve-branch-name
-        run: echo "::set-output name=branch_name::$(REF=${GITHUB_HEAD_REF:-$GITHUB_REF} && echo ${REF#refs/heads/} | sed 's/\//-/g')"
+        run: echo "branch_name=$(REF=${GITHUB_HEAD_REF:-$GITHUB_REF} && echo ${REF#refs/heads/} | sed 's/\//-/g')" >> $GITHUB_OUTPUT
 
       - name: Retrieve git SHA-8 string
         id: retrieve-git-sha-8
-        run: echo "::set-output name=sha8::$(echo ${GITHUB_SHA} | cut -c1-8)"
+        run: echo "sha8=$(echo ${GITHUB_SHA} | cut -c1-8)" >> $GITHUB_OUTPUT
 
       - name: Upload build as artifact
         uses: actions/upload-artifact@v3
@@ -847,7 +915,7 @@ jobs:
           - Download [development build](https://storage.googleapis.com/ampwp_github_artifacts/${{ github.ref }}/dev/amp.zip?${{ github.sha }})
           - Download [production build](https://storage.googleapis.com/ampwp_github_artifacts/${{ github.ref }}/prod/amp.zip?${{ github.sha }})"
           body="${body//$'\n'/'%0A'}"
-          echo "::set-output name=body::$body"
+          echo "body=$body" >> $GITHUB_OUTPUT
 
       - name: Create comment on PR with links to plugin builds
         if: ${{ steps.find-comment.outputs.comment-id == '' }}
diff --git a/.github/workflows/gutenberg-packages-update.yml b/.github/workflows/gutenberg-packages-update.yml
index 1047af3596f..634dfc5795d 100644
--- a/.github/workflows/gutenberg-packages-update.yml
+++ b/.github/workflows/gutenberg-packages-update.yml
@@ -28,7 +28,7 @@ jobs:
     steps:
       - name: Get latest release version
         id: latest-release
-        run: echo "::set-output name=version::$(gh api -X GET repos/wordpress/gutenberg/releases/latest --jq '.name')"
+        run: echo "version=$(gh api -X GET repos/wordpress/gutenberg/releases/latest --jq '.name')" >> $GITHUB_OUTPUT
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
@@ -40,7 +40,7 @@ jobs:
           if ! egrep -q '^[0-9][0-9]*(\.[0-9][0-9]*)*$' <<< "$LAST_VERSION"; then
             LAST_VERSION='0.0.0'
           fi
-          echo "::set-output name=version::$(echo "$LAST_VERSION")"
+          echo "version=$(echo "$LAST_VERSION")" >> $GITHUB_OUTPUT
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           QUERY: 'repo:ampproject/amp-wp is:pr author:app/github-actions is:merged in:title Update Gutenberg packages after'
@@ -50,7 +50,7 @@ jobs:
         run: |
           echo "Last version: $LAST_VER"
           echo "Latest version: $LATEST_VER"
-          echo "::set-output name=outdated::$(php -r 'echo json_encode(version_compare($argv[1], $argv[2], ">"));' "$LATEST_VER" "$LAST_VER")"
+          echo "outdated=$(php -r 'echo json_encode(version_compare($argv[1], $argv[2], ">"));' "$LATEST_VER" "$LAST_VER")" >> $GITHUB_OUTPUT
         env:
           LAST_VER: ${{ steps.last-release.outputs.version }}
           LATEST_VER: ${{ steps.latest-release.outputs.version }}
@@ -66,7 +66,7 @@ jobs:
         id: latest-pr
         run: |
           PR_NUM=$(gh api -X GET search/issues -f q='${{ env.QUERY }}' -f sort='created' -f order='desc' --jq '.items.[0].number')
-          echo "::set-output name=num::$(echo $PR_NUM)"
+          echo "num=$(echo $PR_NUM)" >> $GITHUB_OUTPUT
           echo "Latest PR number: ${PR_NUM}"
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
@@ -100,8 +100,8 @@ jobs:
       - name: Determine branch name
         id: branches
         run: |
-          echo "::set-output name=base::$(echo ${GITHUB_REF#refs/heads/})"
-          echo "::set-output name=head::$(echo "update/gutenberg-v$VERSION-packages")"
+          echo "base=$(echo ${GITHUB_REF#refs/heads/})" >> $GITHUB_OUTPUT
+          echo "head=$(echo "update/gutenberg-v$VERSION-packages")" >> $GITHUB_OUTPUT
         env:
           VERSION: ${{ needs.check-gutenberg-release.outputs.latest-version }}
 
@@ -118,7 +118,7 @@ jobs:
 
       - name: Check if remote branch exists
         id: remote-branch
-        run: echo ::set-output name=exists::$([[ -z $(git ls-remote --heads origin "$HEAD_BRANCH" ) ]] && echo "0" || echo "1")
+        run: echo "exists=$([[ -z $(git ls-remote --heads origin "$HEAD_BRANCH" ) ]] && echo "0" || echo "1")" >> $GITHUB_OUTPUT
         env:
           HEAD_BRANCH: ${{ steps.branches.outputs.head }}
 
@@ -147,7 +147,7 @@ jobs:
         run: |
           # Get list of latest package versions.
           PACKAGES=$(npm outdated --parseable | cut -d':' -f 4 | grep @wordpress | paste -s -d' ' || echo 0)
-          echo "::set-output name=list::$(echo "$PACKAGES")"
+          echo "list=$(echo "$PACKAGES")" >> $GITHUB_OUTPUT
 
       - name: Update packages
         if: steps.packages.outputs.list != 0
diff --git a/.wp-env.json b/.wp-env.json
index 79e357d0fe5..16680193acb 100644
--- a/.wp-env.json
+++ b/.wp-env.json
@@ -1,5 +1,6 @@
 {
   "core": "WordPress/WordPress#master",
+  "phpVersion": "7.4",
   "env": {
     "development": {
       "plugins": [
diff --git a/package.json b/package.json
index cd13fa21479..70b25f6fbf5 100644
--- a/package.json
+++ b/package.json
@@ -143,6 +143,7 @@
     "test:js:update-snapshots": "npm run test:js -- --updateSnapshot",
     "test:js:watch": "npm run test:js -- --watch",
     "test:php": "wp-env run phpunit 'env WP_PHPUNIT__TESTS_CONFIG=/wordpress-phpunit/wp-tests-config.php WORDPRESS_TABLE_PREFIX=wptests_ WP_TESTS_DIR=/var/www/wordpress-develop/tests/phpunit /var/www/html/wp-content/plugins/amp/vendor/bin/phpunit -c /var/www/html/wp-content/plugins/amp/phpunit.xml.dist $npm_config_args'",
+    "test:php:multisite": "wp-env run phpunit 'env WP_MULTISITE=1 WP_PHPUNIT__TESTS_CONFIG=/wordpress-phpunit/wp-tests-config.php WORDPRESS_TABLE_PREFIX=wptests_ WP_TESTS_DIR=/var/www/wordpress-develop/tests/phpunit /var/www/html/wp-content/plugins/amp/vendor/bin/phpunit -c /var/www/html/wp-content/plugins/amp/phpunit.xml.dist $npm_config_args'",
     "test:php:xdebug": "wp-env run tests-wordpress 'env PHP_IDE_CONFIG=serverName=localhost WORDPRESS_TABLE_PREFIX=wptests_ WP_TESTS_DIR=/var/www/wordpress-develop/tests/phpunit WP_PHPUNIT__TESTS_CONFIG=/wordpress-phpunit/wp-tests-config.php /var/www/html/wp-content/plugins/amp/vendor/bin/phpunit -c /var/www/html/wp-content/plugins/amp/phpunit.xml.dist $npm_config_args'",
     "test:php:help": "npm run test:php --args='--help'",
     "update-wordpress-packages": "npm i $(npm outdated --parseable | cut -d':' -f 4 | grep @wordpress)",
diff --git a/src/Admin/AfterActivationSiteScan.php b/src/Admin/AfterActivationSiteScan.php
index 30593edeba9..1425505c1e8 100644
--- a/src/Admin/AfterActivationSiteScan.php
+++ b/src/Admin/AfterActivationSiteScan.php
@@ -211,7 +211,7 @@ protected function get_amp_compatible_plugins_url() {
 	 * @return string URL to AMP compatible themes directory.
 	 */
 	protected function get_amp_compatible_themes_url() {
-		if ( current_user_can( 'switch_themes' ) ) {
+		if ( current_user_can( 'install_themes' ) ) {
 			return admin_url( '/theme-install.php?browse=amp-compatible' );
 		}
 
diff --git a/tests/php/src/Admin/AfterActivationSiteScanTest.php b/tests/php/src/Admin/AfterActivationSiteScanTest.php
index 1095eda22bf..9b5152989b7 100644
--- a/tests/php/src/Admin/AfterActivationSiteScanTest.php
+++ b/tests/php/src/Admin/AfterActivationSiteScanTest.php
@@ -15,6 +15,7 @@
 use AmpProject\AmpWP\Services;
 use AmpProject\AmpWP\Tests\DependencyInjectedTestCase;
 use AmpProject\AmpWP\Tests\Helpers\PrivateAccess;
+use AmpProject\AmpWP\Tests\Helpers\MockAdminUser;
 use AMP_Validation_Manager;
 
 /**
@@ -28,7 +29,7 @@
  */
 class AfterActivationSiteScanTest extends DependencyInjectedTestCase {
 
-	use PrivateAccess;
+	use PrivateAccess, MockAdminUser;
 
 	/**
 	 * Test instance.
@@ -276,7 +277,7 @@ function ( $caps, $cap ) {
 	 * @covers ::get_amp_compatible_plugins_url
 	 */
 	public function test_get_amp_compatible_plugins_url() {
-		wp_set_current_user( self::factory()->user->create( [ 'role' => 'administrator' ] ) );
+		$this->mock_admin_user();
 		$this->assertStringContainsString( '/plugin-install.php?tab=amp-compatible', $this->call_private_method( $this->after_activation_site_scan, 'get_amp_compatible_plugins_url' ) );
 
 		wp_set_current_user( self::factory()->user->create( [ 'role' => 'author' ] ) );
@@ -287,7 +288,7 @@ public function test_get_amp_compatible_plugins_url() {
 	 * @covers ::get_amp_compatible_themes_url
 	 */
 	public function test_get_amp_compatible_themes_url() {
-		wp_set_current_user( self::factory()->user->create( [ 'role' => 'administrator' ] ) );
+		$this->mock_admin_user();
 		$this->assertStringContainsString( '/theme-install.php?browse=amp-compatible', $this->call_private_method( $this->after_activation_site_scan, 'get_amp_compatible_themes_url' ) );
 
 		wp_set_current_user( self::factory()->user->create( [ 'role' => 'author' ] ) );
diff --git a/tests/php/src/Admin/ReaderThemesTest.php b/tests/php/src/Admin/ReaderThemesTest.php
index b38d9090f55..b8e8d4ef2e5 100644
--- a/tests/php/src/Admin/ReaderThemesTest.php
+++ b/tests/php/src/Admin/ReaderThemesTest.php
@@ -15,6 +15,7 @@
 use AmpProject\AmpWP\Option;
 use AmpProject\AmpWP\Tests\Helpers\LoadsCoreThemes;
 use AmpProject\AmpWP\Tests\Helpers\ThemesApiRequestMocking;
+use AmpProject\AmpWP\Tests\Helpers\MockAdminUser;
 use AmpProject\AmpWP\Tests\TestCase;
 use Closure;
 use WP_Error;
@@ -28,7 +29,7 @@
  */
 class ReaderThemesTest extends TestCase {
 
-	use ThemesApiRequestMocking, LoadsCoreThemes;
+	use ThemesApiRequestMocking, LoadsCoreThemes, MockAdminUser;
 
 	/**
 	 * Test instance.
@@ -304,7 +305,8 @@ static function () {
 			}
 		);
 
-		wp_set_current_user( $this->factory()->user->create( [ 'role' => 'administrator' ] ) );
+		$this->mock_admin_user();
+
 		$expected = $get_expected();
 		$this->assertEquals( $expected, $this->reader_themes->get_theme_availability( $theme ) );
 		$this->assertEquals( $can_install, $this->reader_themes->can_install_theme( $theme ) );
@@ -344,7 +346,7 @@ static function () {
 		$this->assertFalse( $this->reader_themes->can_install_theme( $core_theme ) );
 		$this->assertFalse( $this->reader_themes->can_install_theme( $neve_theme ) );
 
-		wp_set_current_user( self::factory()->user->create( [ 'role' => 'administrator' ] ) );
+		$this->mock_admin_user();
 		$this->assertTrue( $this->reader_themes->can_install_theme( $core_theme ) );
 		$this->assertTrue( $this->reader_themes->can_install_theme( $neve_theme ) );
 
diff --git a/tests/php/src/Admin/SiteHealthTest.php b/tests/php/src/Admin/SiteHealthTest.php
index bdf9f54c562..ce1fc2a0a7b 100644
--- a/tests/php/src/Admin/SiteHealthTest.php
+++ b/tests/php/src/Admin/SiteHealthTest.php
@@ -15,6 +15,7 @@
 use AmpProject\AmpWP\QueryVar;
 use AmpProject\AmpWP\Tests\Helpers\HomeUrlLoopbackRequestMocking;
 use AmpProject\AmpWP\Tests\Helpers\PrivateAccess;
+use AmpProject\AmpWP\Tests\Helpers\MockAdminUser;
 use AmpProject\AmpWP\Tests\TestCase;
 use WP_REST_Server;
 use WP_Error;
@@ -28,6 +29,7 @@ class SiteHealthTest extends TestCase {
 
 	use HomeUrlLoopbackRequestMocking;
 	use PrivateAccess;
+	use MockAdminUser;
 
 	/**
 	 * Whether external object cache is being used.
@@ -139,7 +141,8 @@ public function test_register_async_test_endpoints() {
 		$this->assertFalse( call_user_func( $route['permission_callback'] ) );
 
 		// Prior to WordPress 5.2, the view_site_health_checks cap didn't exist because Site Health didn't exist.
-		wp_set_current_user( self::factory()->user->create( [ 'role' => 'administrator' ] ) );
+		$this->mock_admin_user();
+
 		if ( version_compare( get_bloginfo( 'version' ), '5.2', '>=' ) ) {
 			$this->assertTrue( call_user_func( $route['permission_callback'] ) );
 		} else {
diff --git a/tests/php/src/Admin/SupportLinkTest.php b/tests/php/src/Admin/SupportLinkTest.php
index 624a8de3c87..32ef491f078 100644
--- a/tests/php/src/Admin/SupportLinkTest.php
+++ b/tests/php/src/Admin/SupportLinkTest.php
@@ -13,6 +13,7 @@
 use AMP_Validation_Manager;
 use AMP_Theme_Support;
 use AMP_Validated_URL_Post_Type;
+use AmpProject\AmpWP\Tests\Helpers\MockAdminUser;
 use AmpProject\AmpWP\Tests\TestCase;
 
 /**
@@ -23,6 +24,8 @@
  */
 class SupportLinkTest extends TestCase {
 
+	use MockAdminUser;
+
 	/**
 	 * Instance of SupportLink
 	 *
@@ -65,7 +68,7 @@ public function test_is_needed() {
 		$this->assertFalse( SupportLink::is_needed() );
 
 		// Test 2: Test with admin user.
-		wp_set_current_user( self::factory()->user->create( [ 'role' => 'administrator' ] ) );
+		$this->mock_admin_user();
 
 		$this->assertTrue( SupportLink::is_needed() );
 	}
diff --git a/tests/php/src/Admin/SupportScreenTest.php b/tests/php/src/Admin/SupportScreenTest.php
index c3f76fe86cb..ec28a045214 100644
--- a/tests/php/src/Admin/SupportScreenTest.php
+++ b/tests/php/src/Admin/SupportScreenTest.php
@@ -15,6 +15,7 @@
 use AmpProject\AmpWP\Infrastructure\Registerable;
 use AmpProject\AmpWP\Infrastructure\Service;
 use AmpProject\AmpWP\Tests\DependencyInjectedTestCase;
+use AmpProject\AmpWP\Tests\Helpers\MockAdminUser;
 use AmpProject\AmpWP\Tests\Helpers\HomeUrlLoopbackRequestMocking;
 
 /**
@@ -25,7 +26,7 @@
  */
 class SupportScreenTest extends DependencyInjectedTestCase {
 
-	use HomeUrlLoopbackRequestMocking;
+	use HomeUrlLoopbackRequestMocking, MockAdminUser;
 
 	/**
 	 * Instance of SupportMenu
@@ -119,7 +120,8 @@ public function test_is_needed() {
 		$this->assertFalse( SupportScreen::has_cap() );
 
 		// Mock the is_admin() with required user caps.
-		wp_set_current_user( self::factory()->user->create( [ 'role' => 'administrator' ] ) );
+		$this->mock_admin_user();
+
 		$this->assertFalse( SupportScreen::is_needed() );
 		$this->assertTrue( SupportScreen::has_cap() );
 
diff --git a/tests/php/src/Admin/UserRESTEndpointExtensionTest.php b/tests/php/src/Admin/UserRESTEndpointExtensionTest.php
index fd02e2933c0..ae2828504dc 100644
--- a/tests/php/src/Admin/UserRESTEndpointExtensionTest.php
+++ b/tests/php/src/Admin/UserRESTEndpointExtensionTest.php
@@ -9,6 +9,7 @@
 
 use AMP_Theme_Support;
 use AmpProject\AmpWP\Admin\UserRESTEndpointExtension;
+use AmpProject\AmpWP\Tests\Helpers\MockAdminUser;
 use AmpProject\AmpWP\Tests\TestCase;
 use WP_REST_Request;
 
@@ -23,6 +24,8 @@
  */
 class UserRESTEndpointExtensionTest extends TestCase {
 
+	use MockAdminUser;
+
 	/**
 	 * Test instance.
 	 *
@@ -68,7 +71,8 @@ public function test_update_review_panel_dismissed_for_template_mode() {
 		$server = rest_get_server();
 		$this->user_rest_endpoint_extension->register_rest_field();
 
-		$admin_user  = self::factory()->user->create_and_get( [ 'role' => 'administrator' ] );
+		$admin_user = $this->mock_admin_user();
+
 		$editor_user = self::factory()->user->create_and_get( [ 'role' => 'editor' ] );
 
 		$this->assertSame( '', $this->user_rest_endpoint_extension->get_review_panel_dismissed_for_template_mode( [ 'id' => $admin_user->ID ] ) );
diff --git a/tests/php/src/Helpers/MockAdminUser.php b/tests/php/src/Helpers/MockAdminUser.php
new file mode 100644
index 00000000000..45debbea1a1
--- /dev/null
+++ b/tests/php/src/Helpers/MockAdminUser.php
@@ -0,0 +1,35 @@
+<?php
+/**
+ * Trait MockAdminUser.
+ *
+ * @package AmpProject\AmpWP
+ */
+
+namespace AmpProject\AmpWP\Tests\Helpers;
+
+/**
+ * Helper trait for mocking an user:
+ * - Admin user in single site.
+ * - Super admin user in multisite.
+ *
+ * @package AmpProject\AmpWP
+ */
+trait MockAdminUser {
+
+	/**
+	 * Mock an admin or super admin user.
+	 *
+	 * @return WP_User
+	 */
+	public function mock_admin_user() {
+		$admin_user = self::factory()->user->create_and_get( [ 'role' => 'administrator' ] );
+
+		if ( is_multisite() ) {
+			grant_super_admin( $admin_user->ID );
+		}
+
+		wp_set_current_user( $admin_user->ID );
+
+		return $admin_user;
+	}
+}
diff --git a/tests/php/src/ReaderThemeLoaderTest.php b/tests/php/src/ReaderThemeLoaderTest.php
index a0a583eade9..c58700aef9c 100644
--- a/tests/php/src/ReaderThemeLoaderTest.php
+++ b/tests/php/src/ReaderThemeLoaderTest.php
@@ -10,6 +10,7 @@
 use AmpProject\AmpWP\Option;
 use AmpProject\AmpWP\ReaderThemeLoader;
 use AmpProject\AmpWP\Tests\Helpers\LoadsCoreThemes;
+use AmpProject\AmpWP\Tests\Helpers\MockAdminUser;
 use WP_Customize_Manager;
 use WP_Customize_Panel;
 use WP_Theme;
@@ -17,7 +18,7 @@
 /** @coversDefaultClass \AmpProject\AmpWP\ReaderThemeLoader */
 final class ReaderThemeLoaderTest extends DependencyInjectedTestCase {
 
-	use LoadsCoreThemes;
+	use LoadsCoreThemes, MockAdminUser;
 
 	/** @var ReaderThemeLoader */
 	private $instance;
@@ -151,12 +152,18 @@ public function test_filter_wp_prepare_themes_to_indicate_reader_theme() {
 		AMP_Options_Manager::update_option( Option::READER_THEME, $reader_theme_slug );
 		$this->assertEquals( $active_theme_slug, get_stylesheet() );
 		$this->assertEquals( $reader_theme_slug, $this->instance->get_reader_theme()->get_stylesheet() );
-		wp_set_current_user( self::factory()->user->create( [ 'role' => 'administrator' ] ) );
+
+		$this->mock_admin_user();
 
 		// Note that this is added via filter and not called directly because the filtered value is keyed by theme slug,
 		// but the return value of wp_prepare_themes_for_js() is keyed with numeric indices.
 		$this->instance->register(); // This adds a `wp_prepare_themes_for_js` filter.
-		$themes = wp_prepare_themes_for_js();
+		$themes = wp_prepare_themes_for_js(
+			[
+				wp_get_theme( $active_theme_slug ),
+				wp_get_theme( $reader_theme_slug ),
+			]
+		);
 		$this->assertEquals( $active_theme_slug, $themes[0]['id'] );
 		$this->assertStringNotContainsString( 'AMP', $themes[0]['description'] );
 		$this->assertArrayHasKey( 'delete', $themes[0]['actions'], 'The delete key is expected even though the theme is active because the delete option is hidden via the JS template.' );
diff --git a/tests/php/test-amp-helper-functions.php b/tests/php/test-amp-helper-functions.php
index ebcc2d4a6e4..aafa5a37801 100644
--- a/tests/php/test-amp-helper-functions.php
+++ b/tests/php/test-amp-helper-functions.php
@@ -10,6 +10,7 @@
 use AmpProject\AmpWP\Tests\Helpers\HandleValidation;
 use AmpProject\AmpWP\Tests\Helpers\LoadsCoreThemes;
 use AmpProject\AmpWP\Tests\Helpers\PrivateAccess;
+use AmpProject\AmpWP\Tests\Helpers\MockAdminUser;
 use AmpProject\AmpWP\Tests\DependencyInjectedTestCase;
 use AmpProject\AmpWP\AmpSlugCustomizationWatcher;
 
@@ -21,6 +22,7 @@ class Test_AMP_Helper_Functions extends DependencyInjectedTestCase {
 	use HandleValidation;
 	use LoadsCoreThemes;
 	use PrivateAccess;
+	use MockAdminUser;
 
 	/**
 	 * The mock Site Icon value to use in a filter.
@@ -1963,7 +1965,7 @@ function ( $xpaths ) use ( $element_xpaths ) {
 		remove_filter( 'amp_dev_mode_enabled', '__return_true' );
 
 		// Check that AMP_Dev_Mode_Sanitizer is registered once in dev mode, and now also with admin bar showing.
-		wp_set_current_user( self::factory()->user->create( [ 'role' => 'administrator' ] ) );
+		$this->mock_admin_user();
 		add_filter( 'amp_dev_mode_enabled', '__return_true' );
 		add_filter( 'show_admin_bar', '__return_true' );
 		$sanitizers = amp_get_content_sanitizers();
@@ -2576,6 +2578,11 @@ public function data_amp_has_paired_endpoint() {
 	 * @param bool   $is_amp
 	 */
 	public function test_amp_has_paired_endpoint_go_to( $paired_url_structure, $suffix, $is_amp ) {
+		if ( is_multisite() ) {
+			// Switch blog in multisite to ensure paired endpoint is working with multiple subdirectory installations.
+			switch_to_blog( self::factory()->blog->create() );
+		}
+
 		AMP_Options_Manager::update_option( Option::PAIRED_URL_STRUCTURE, $paired_url_structure );
 
 		add_filter( 'wp_redirect', '__return_empty_string' ); // Prevent ensure_proper_amp_location() from redirecting.
diff --git a/tests/php/test-uninstall.php b/tests/php/test-uninstall.php
index e2c4167c3da..8b27356731d 100644
--- a/tests/php/test-uninstall.php
+++ b/tests/php/test-uninstall.php
@@ -569,7 +569,17 @@ public function test_remove_plugin_data() {
 		$num_queries_before = $wpdb->num_queries;
 		require AMP__DIR__ . '/uninstall.php';
 		$this->flush_cache();
-		$this->assertEquals( $num_queries_before, $wpdb->num_queries );
+
+		if ( is_multisite() ) {
+			/*
+			 * Multisite has 2 additional queries:
+			 * 1. Get sites query.
+			 * 2. Switch to blog query.
+			 */
+			$this->assertEquals( $num_queries_before + 2, $wpdb->num_queries );
+		} else {
+			$this->assertEquals( $num_queries_before, $wpdb->num_queries );
+		}
 
 		$this->assertNotEmpty( get_option( AMP_Options_Manager::OPTION_NAME, false ) );