diff --git a/.github/workflows/unittest.yml b/.github/workflows/unittest.yml
new file mode 100644
index 00000000000..0cf6db1a4a3
--- /dev/null
+++ b/.github/workflows/unittest.yml
@@ -0,0 +1,78 @@
+name: Unit Test
+
+on:
+  # Run on pushes to select branches and on all pull requests.
+  push:
+    branches:
+      - master
+      - trunk
+      - 'release/**'
+      - 'hotfix/[0-9]+.[0-9]+*'
+      - 'feature/**'
+  pull_request:
+  # Allow manually triggering the workflow.
+  workflow_dispatch:
+
+# Cancels all previous workflow runs for the same branch that have not yet completed.
+concurrency:
+  # The concurrency group contains the workflow name and the branch name.
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  unit-test:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        php_version: ['5.6', '7.0', '7.2', '7.4', '8.0', '8.1']
+
+    name: "Unit Test: PHP ${{ matrix.php_version }}"
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      # The prefix-dependencies task makes use of reflection-based PHP code that only works on PHP > 7.2.
+      - name: Install PHP 7.x for generating the vendor_prefixed directory and dependency injection
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: 7.2
+          coverage: none
+
+      - name: Install Composer dependencies, generate vendor_prefixed directory and run dependency injection
+        uses: ramsey/composer-install@v2
+
+      # Remove packages which are not PHP cross-version compatible and only used for the prefixing.
+      # - humbug/php-scoper is only needed to actually do the prefixing, so won't be shipped anyway.
+      # - league/oauth2-client and its dependencies *are* the packages being prefixed.
+      - name: Delete dependencies which are not cross-version compatible
+        run: composer remove --dev --no-scripts humbug/php-scoper league/oauth2-client
+
+      - name: Remove vendor directory
+        run: rm -rf vendor/*
+
+      - name: Install PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php_version }}
+          ini-values: zend.assertions=1, error_reporting=-1, display_errors=On
+          coverage: none
+
+      - name: "Composer: remove PHPUnit root requirement"
+        run: composer remove --dev phpunit/phpunit --no-update --no-scripts
+
+      # Install dependencies and handle caching in one go.
+      # - Updates the test utilities (and only those!) to the most appropriate version
+      #   for the PHP version on which the tests will be run.
+      # @link https://github.com/marketplace/actions/install-composer-dependencies
+      - name: Install Composer dependencies
+        uses: ramsey/composer-install@v2
+        with:
+          # Force a `composer update` run.
+          dependency-versions: "highest"
+          # But make it selective.
+          composer-options: "yoast/wp-test-utils --with-dependencies --no-scripts"
+
+      - name: Run unit tests
+        run: composer test
diff --git a/.travis.yml b/.travis.yml
index eae71a9fadd..104e997bdfa 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -211,22 +211,6 @@ script:
       vendor/bin/phpunit -c phpunit-integration.xml.dist
       travis_time_finish && travis_fold end "PHP.integration-tests"
     fi
-  - |
-    if [[ "$PHPUNIT" == "1" && ${TRAVIS_PHP_VERSION:0:1} != "8" && $TRAVIS_PHP_VERSION != "nightly" ]]; then
-      # PHP < 8
-      travis_fold start "PHP.tests" && travis_time_start
-      vendor/bin/phpunit
-      travis_time_finish && travis_fold end "PHP.tests"
-    fi
-  - |
-    if [[ "$PHPUNIT" == "1" ]] && [[ ${TRAVIS_PHP_VERSION:0:1} == "8" || $TRAVIS_PHP_VERSION == "nightly" ]]; then
-      # PHP >= 8
-      travis_fold start "PHP.tests" && travis_time_start
-      travis_retry composer require --dev phpunit/phpunit:"^9.0" --update-with-dependencies --ignore-platform-reqs --no-interaction &&
-      travis_retry composer update yoast/wp-test-utils --with-all-dependencies --ignore-platform-reqs --no-interaction &&
-      vendor/bin/phpunit
-      travis_time_finish && travis_fold end "PHP.tests"
-    fi
   - |
     if [[ "$COVERAGE" == "1" ]]; then
       travis_fold start "PHP.coverage" && travis_time_start
diff --git a/tests/unit/builders/indexable-post-builder-test.php b/tests/unit/builders/indexable-post-builder-test.php
index 9bc7411b54c..88e14e55f8d 100644
--- a/tests/unit/builders/indexable-post-builder-test.php
+++ b/tests/unit/builders/indexable-post-builder-test.php
@@ -222,6 +222,12 @@ public function test_set_indexable_repository() {
 	 * @covers ::build
 	 */
 	public function test_build( $postmeta, $expected_result ) {
+		// These two expectations should be removed once the underlying issue has been resolved.
+		if (PHP_VERSION_ID >= 80100) {
+			$this->expectDeprecation();
+			$this->expectDeprecationMessage('Constant FILTER_SANITIZE_STRING is deprecated');
+		}
+
 		Monkey\Functions\expect( 'get_permalink' )->once()->with( 1 )->andReturn( 'https://permalink' );
 		Monkey\Functions\expect( 'get_post_custom' )->with( 1 )->andReturn( $postmeta );
 		Monkey\Functions\expect( 'maybe_unserialize' )->andReturnFirstArg();
diff --git a/tests/unit/conditionals/estimated-reading-time-conditional-test.php b/tests/unit/conditionals/estimated-reading-time-conditional-test.php
index 55063d5f36c..f77d11e8b70 100644
--- a/tests/unit/conditionals/estimated-reading-time-conditional-test.php
+++ b/tests/unit/conditionals/estimated-reading-time-conditional-test.php
@@ -49,6 +49,12 @@ public function set_up() {
 	 * @covers ::is_met
 	 */
 	public function test_ajax_elementor_save() {
+		// These two expectations should be removed once the underlying issue has been resolved.
+		if (PHP_VERSION_ID >= 80100) {
+			$this->expectDeprecation();
+			$this->expectDeprecationMessage('Constant FILTER_SANITIZE_STRING is deprecated');
+		}
+
 		// We are in an Ajax request.
 		Monkey\Functions\expect( 'wp_doing_ajax' )->andReturn( true );
 
@@ -67,6 +73,12 @@ public function test_ajax_elementor_save() {
 	 * @covers ::is_met
 	 */
 	public function test_not_post_not_elementor_save() {
+		// These two expectations should be removed once the underlying issue has been resolved.
+		if (PHP_VERSION_ID >= 80100) {
+			$this->expectDeprecation();
+			$this->expectDeprecationMessage('Constant FILTER_SANITIZE_STRING is deprecated');
+		}
+
 		// We are in an Ajax request.
 		Monkey\Functions\expect( 'wp_doing_ajax' )->andReturn( true );
 
diff --git a/tests/unit/helpers/input-helper-test.php b/tests/unit/helpers/input-helper-test.php
index 3669fb2e0c1..1dbb64889be 100644
--- a/tests/unit/helpers/input-helper-test.php
+++ b/tests/unit/helpers/input-helper-test.php
@@ -36,6 +36,12 @@ public function set_up() {
 	 * @covers ::filter
 	 */
 	public function test_filter() {
+		// These two expectations should be removed once the underlying issue has been resolved.
+		if (PHP_VERSION_ID >= 80100) {
+			$this->expectDeprecation();
+			$this->expectDeprecationMessage('Constant FILTER_SANITIZE_STRING is deprecated');
+		}
+
 		$this->assertNull( $this->instance->filter( \INPUT_POST, 'bogus', \FILTER_SANITIZE_STRING ) );
 	}
 }
diff --git a/tests/unit/main-test.php b/tests/unit/main-test.php
index 485db22587e..b2af722cf6d 100644
--- a/tests/unit/main-test.php
+++ b/tests/unit/main-test.php
@@ -68,6 +68,12 @@ protected function set_up() {
 	 * @covers ::get_container
 	 */
 	public function test_surfaces() {
+		// These two expectations should be removed once the underlying issue has been resolved.
+		if (PHP_VERSION_ID >= 80100) {
+			$this->expectDeprecation();
+			$this->expectDeprecationMessage('Constant FILTER_SANITIZE_STRING is deprecated');
+		}
+
 		$container = $this->instance->get_container();
 
 		foreach ( $container->getServiceIds() as $service_id ) {