diff --git a/.github/workflows/cs-lint.yml b/.github/workflows/cs-lint.yml
index fe4dac4a7..fbed4369f 100644
--- a/.github/workflows/cs-lint.yml
+++ b/.github/workflows/cs-lint.yml
@@ -37,7 +37,7 @@ jobs:
         uses: korelstar/xmllint-problem-matcher@v1
 
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       # Validate the composer.json file.
       # @link https://getcomposer.org/doc/03-cli.md#validate
@@ -45,11 +45,11 @@ jobs:
         run: composer validate --no-check-all
 
       # Install dependencies and handle caching in one go.
-      # @link https://github.com/marketplace/actions/install-composer-dependencies
-      - name: Install Composer dependencies
-        uses: ramsey/composer-install@v1
-
+      # @link https://github.com/marketplace/actions/install-php-dependencies-with-composer
+      - name: Install PHP Dependencies with Composer
+        uses: ramsey/composer-install@2.2.0
       # Lint PHP.
+      
       - name: Lint PHP against parse errors
         run: composer lint-ci | cs2pr
 
diff --git a/bin/install-wp-tests.sh b/bin/install-wp-tests.sh
index 7a45293af..dc8366c63 100755
--- a/bin/install-wp-tests.sh
+++ b/bin/install-wp-tests.sh
@@ -108,8 +108,8 @@ install_test_suite() {
 		# set up testing suite
 		mkdir -p $WP_TESTS_DIR
 		rm -rf $WP_TESTS_DIR/{includes,data}
-		svn export --quiet --ignore-externals https://develop.svn.wordpress.org/${WP_TESTS_TAG}/tests/phpunit/includes/ $WP_TESTS_DIR/includes
-		svn export --quiet --ignore-externals https://develop.svn.wordpress.org/${WP_TESTS_TAG}/tests/phpunit/data/ $WP_TESTS_DIR/data
+		svn export --ignore-externals https://develop.svn.wordpress.org/${WP_TESTS_TAG}/tests/phpunit/includes/ $WP_TESTS_DIR/includes
+		svn export --ignore-externals https://develop.svn.wordpress.org/${WP_TESTS_TAG}/tests/phpunit/data/ $WP_TESTS_DIR/data
 	fi
 
 	if [ ! -f wp-tests-config.php ]; then
diff --git a/composer.json b/composer.json
index dfb2b6027..e1f47f820 100644
--- a/composer.json
+++ b/composer.json
@@ -16,13 +16,13 @@
 	},
 	"require-dev": {
 		"automattic/vipwpcs": "^2.2",
-		"dealerdirect/phpcodesniffer-composer-installer": "^0.4.1 || ^0.5 || ^0.6.2 || ^0.7",
+		"dealerdirect/phpcodesniffer-composer-installer": "^1.0",
 		"php-parallel-lint/php-parallel-lint": "^1.0",
 		"phpcompatibility/phpcompatibility-wp": "^2.1",
-		"phpunit/phpunit": "^4 || ^5 || ^6 || ^7",
+		"phpunit/phpunit": "^9",
 		"squizlabs/php_codesniffer": "^3.5",
 		"wp-coding-standards/wpcs": "^2.3.0",
-		"yoast/phpunit-polyfills": "^0.2.0"
+		"yoast/phpunit-polyfills": "^2.0"
 	},
 	"scripts": {
 		"coverage": [
@@ -57,5 +57,11 @@
 	"support": {
 		"issues": "https://github.com/Automattic/msm-sitemap/issues",
 		"source": "https://github.com/Automattic/msm-sitemap"
+	},
+	"config": {
+		"allow-plugins": {
+			"composer/installers": true,
+			"dealerdirect/phpcodesniffer-composer-installer": true
+		}
 	}
 }
diff --git a/tests/test-sitemap--cron.php b/tests/test-sitemap--cron.php
index 82dc2c493..357603eba 100644
--- a/tests/test-sitemap--cron.php
+++ b/tests/test-sitemap--cron.php
@@ -31,7 +31,7 @@ class WP_Test_Sitemap_Cron extends WP_UnitTestCase {
 	/**
 	 * Generate posts and build the sitemap
 	 */
-	function setup() {
+	function setup(): void {
 		if ( ! class_exists( 'MSM_Sitemap_Builder_Cron' ) ) {
 			require dirname( dirname( __FILE__ ) ) . '/includes/msm-sitemap-builder-cron.php';
 			MSM_Sitemap_Builder_Cron::setup();
@@ -55,7 +55,7 @@ function setup() {
 	/**
 	 * Remove the sample posts and the sitemap posts
 	 */
-	function teardown() {
+	function teardown(): void {
 		$this->test_base->posts = array();
 		$sitemaps = get_posts( array(
 			'post_type' => Metro_Sitemap::SITEMAP_CPT,
@@ -98,7 +98,7 @@ function test_cron_jobs_scheduling() {
 		$years_being_processed = (array) get_option( 'msm_years_to_process', array() );
 
 		// Validate Current Month is added to months_to_process.
-		$month = date( 'n', time() );
+		$month = (int) date( 'n', time() );
 		$this->assertContains( $month, $months_being_processed, 'Initial Year Processing should use Current Month if same year' );
 
 		// fake_cron.
diff --git a/tests/test-sitemap-cpt.php b/tests/test-sitemap-cpt.php
index f3d403ec5..1ea608ac8 100644
--- a/tests/test-sitemap-cpt.php
+++ b/tests/test-sitemap-cpt.php
@@ -31,7 +31,7 @@ class WP_Test_Sitemap_CPT extends WP_UnitTestCase {
 	/**
 	 * Initialize Test CPT
 	 */
-	static function setupBeforeClass() {
+	static function setupBeforeClass(): void {
 		register_post_type(
 			self::TEST_CPT,
 			array(
@@ -55,7 +55,7 @@ static function setupBeforeClass() {
 	/**
 	 * Initialize MSM_SiteMap_Test
 	 */
-	function setup() {
+	function setup(): void {
 
 		$this->test_base = new MSM_SiteMap_Test();
 
@@ -88,7 +88,7 @@ function setup() {
 	/**
 	 * Remove the sample posts and the sitemap posts
 	 */
-	function teardown() {
+	function teardown(): void {
 		$this->test_base->posts = array();
 		$sitemaps = get_posts( array(
 			'post_type' => Metro_Sitemap::SITEMAP_CPT,
diff --git a/tests/test-sitemap-creation.php b/tests/test-sitemap-creation.php
index 41b6bbe88..3a04a67b3 100644
--- a/tests/test-sitemap-creation.php
+++ b/tests/test-sitemap-creation.php
@@ -32,7 +32,7 @@ class WP_Test_Sitemap_Creation extends WP_UnitTestCase {
 	/**
 	 * Generate posts and build the sitemap
 	 */
-	function setup() {
+	function setup(): void {
 
 		$this->test_base = new MSM_SiteMap_Test();
 
@@ -52,7 +52,7 @@ function setup() {
 	/**
 	 * Remove the sample posts and the sitemap posts
 	 */
-	function teardown() {
+	function teardown(): void {
 		$this->test_base->posts = array();
 		$sitemaps = get_posts( array(
 			'post_type' => Metro_Sitemap::SITEMAP_CPT,
@@ -81,7 +81,7 @@ function test_sitemap_posts_were_created() {
 		foreach ( $sitemaps as $i => $map_id ) {
 			$xml = get_post_meta( $map_id, 'msm_sitemap_xml', true );
 			$post_id = $this->test_base->posts[ $i ]['ID'];
-			$this->assertContains( 'p=' . $post_id, $xml );
+			$this->assertStringContainsString( 'p=' . $post_id, $xml );
 
 			$xml_struct = simplexml_load_string( $xml );
 			$this->assertNotEmpty( $xml_struct->url );
@@ -89,7 +89,7 @@ function test_sitemap_posts_were_created() {
 			$this->assertNotEmpty( $xml_struct->url->lastmod );
 			$this->assertNotEmpty( $xml_struct->url->changefreq );
 			$this->assertNotEmpty( $xml_struct->url->priority );
-			$this->assertContains( 'p=' . $post_id, (string) $xml_struct->url->loc );
+			$this->assertStringContainsString( 'p=' . $post_id, (string) $xml_struct->url->loc );
 
 			$post = get_post( $post_id );
 			setup_postdata( $post );
diff --git a/tests/test-sitemap-filter.php b/tests/test-sitemap-filter.php
index 42db71cca..0b1e99fbc 100644
--- a/tests/test-sitemap-filter.php
+++ b/tests/test-sitemap-filter.php
@@ -23,7 +23,7 @@ function test_bypass_main_query() {
 		// Verify post_pre_query on sitemap queryvar returns empty array
 		set_query_var( 'sitemap', 'true' );
 		$posts = apply_filters_ref_array( 'posts_pre_query', array( null, $wp_query ) );
-		$this->assertInternalType('array', $posts);
+		$this->assertIsArray( $posts );
 		$this->assertEmpty( $posts );
 		
 	}
diff --git a/tests/test-sitemap-functions.php b/tests/test-sitemap-functions.php
index 1ab56a48c..85398ca25 100644
--- a/tests/test-sitemap-functions.php
+++ b/tests/test-sitemap-functions.php
@@ -24,7 +24,7 @@ class WP_Test_Sitemap_Functions extends WP_UnitTestCase {
 	/**
 	 * Initialize MSM_SiteMap_Test
 	 */
-	function setup() {
+	function setup(): void {
 		$this->test_base = new MSM_SiteMap_Test();
 
 	}
@@ -32,7 +32,7 @@ function setup() {
 	/**
 	 * Remove the sample posts and the sitemap posts
 	 */
-	function teardown() {
+	function teardown(): void {
 		$this->test_base->posts = array();
 		$sitemaps = get_posts( array(
 			'post_type' => Metro_Sitemap::SITEMAP_CPT,
@@ -141,12 +141,12 @@ function test_check_year_has_posts() {
 		// Add a post for last year and 5 years ago.
 		$date = strtotime( '-1 year', time() );
 		$cur_day = date( 'Y', $date ) . '-' . date( 'm', $date ) . '-' . date( 'd', $date ) . ' 00:00:00';
-		$prev_year = date( 'Y', $date );
+		$prev_year = (int) date( 'Y', $date );
 		$this->test_base->create_dummy_post( $cur_day );
 
 		$date = strtotime( '-4 year', $date );
 		$cur_day = date( 'Y', $date ) . '-' . date( 'm', $date ) . '-' . date( 'd', $date ) . ' 00:00:00';
-		$prev5_year = date( 'Y', $date );
+		$prev5_year = (int) date( 'Y', $date );
 		$this->test_base->create_dummy_post( $cur_day );
 
 		// Verify only Years for Posts are returned.
diff --git a/tests/test-sitemap-index.php b/tests/test-sitemap-index.php
index f8ae43bf5..979766dbd 100644
--- a/tests/test-sitemap-index.php
+++ b/tests/test-sitemap-index.php
@@ -31,7 +31,7 @@ class WP_Test_Sitemap_Index extends WP_UnitTestCase {
 	/**
 	 * Generate posts and build initial sitemaps
 	 */
-	function setup() {
+	function setup(): void {
 		_delete_all_posts();
 
 		$this->test_base = new MSM_SiteMap_Test();
@@ -54,7 +54,7 @@ function setup() {
 	/**
 	 * Remove created posts, sitemaps and options
 	 */
-	function teardown() {
+	function teardown(): void {
 		$this->test_base->posts = array();
 		$sitemaps = get_posts( array(
 			'post_type' => Metro_Sitemap::SITEMAP_CPT,
diff --git a/tests/test-sitemap-stats.php b/tests/test-sitemap-stats.php
index 6feef637c..cf5d89a77 100644
--- a/tests/test-sitemap-stats.php
+++ b/tests/test-sitemap-stats.php
@@ -32,7 +32,7 @@ class WP_Test_Sitemap_Stats extends WP_UnitTestCase {
 	/**
 	 * Generate posts and build initial sitemaps
 	 */
-	function setup() {
+	function setup(): void {
 		_delete_all_posts();
 
 		$this->test_base = new MSM_SiteMap_Test();
@@ -55,7 +55,7 @@ function setup() {
 	/**
 	 * Remove created posts, Sitemaps and options
 	 */
-	function teardown() {
+	function teardown(): void {
 		$this->test_base->posts = array();
 		$sitemaps = get_posts( array(
 			'post_type' => Metro_Sitemap::SITEMAP_CPT,