Add github action for running tests (#4)

.github/workflows/tests.yml

@@ -0,0 +1,25 @@
+name: Tests
+
+on:
+  push:
+    paths:
+      - '**.php'
+  pull_request:
+    types:
+      - opened
+    paths:
+      - '**.php'
+
+jobs:
+  build-test:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - uses: php-actions/composer@v5
+
+      - name: PHPUnit Tests
+        uses: php-actions/phpunit@v2
+        with:
+          configuration: phpunit.xml