chore: add circleci config

.circleci/config.yml

@@ -0,0 +1,49 @@
+version: 2.1 # Use 2.1 to enable using orbs and other features.
+
+orbs: 
+  php: circleci/[email protected]
+
+jobs:
+  test:
+    parameters:
+      version: 
+        default: "8.0"
+        description: PHP version to install
+        type: string
+    docker:
+      - image: cimg/php:<<parameters.version>>
+    steps:
+      - checkout
+      - php/install-composer
+      - run: composer self-update
+
+      # Print php and composer versions for debugging
+      - run: php --version
+      - run: composer --version
+
+      # although not recommended, we need to update dependencies to work on php8.1
+      - when:
+          condition:
+            equal: [ "8.1", <<parameters.version>> ]
+          steps:
+            - run: composer update
+
+      # install deps
+      - run: composer install
+
+      # run tests
+      - run: 
+          name: PHPUnit Tests
+          command: vendor/bin/phpunit --bootstrap src/autoload.php tests
+
+workflows:
+  version: 2
+  test:
+    jobs:
+      - test:
+          matrix:
+            parameters:
+              version:
+                - "7.4"
+                - "8.0"
+                - "8.1"