Enable CI with GitHub actions (#2)

.github/workflows/tests.yml

@@ -0,0 +1,39 @@
+name: build
+
+on: [push,pull_request]
+
+jobs:
+  build:
+
+    strategy:
+      matrix:
+        php-version:
+          - "7.4"
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: "Installing PHP"
+      uses: "shivammathur/setup-php@v2"
+      with:
+        php-version: "${{ matrix.php-version }}"
+        ini-values: memory_limit=-1
+
+    - name: Get Composer Cache Directory
+      id: composer-cache
+      run: |
+        echo "::set-output name=dir::$(composer config cache-files-dir)"
+    - uses: actions/cache@v2
+      with:
+        path: ${{ steps.composer-cache.outputs.dir }}
+        key: ${{ runner.os }}-${{ matrix.php-version }}-composer-${{ hashFiles('**/composer.lock') }}
+        restore-keys: |
+          ${{ runner.os }}-${{ matrix.php-version }}-composer-
+
+    - name: Install dependencies
+      run: composer install
+
+    - name: Run test suite
+      run: composer build