added GitHub Actions for tests

.github/workflows/tests.yml

@@ -0,0 +1,66 @@
+name: Tests
+
+on: [push, pull_request]
+
+jobs:
+    tests:
+        runs-on: ubuntu-latest
+        strategy:
+            matrix:
+                php: ['7.1', '7.2', '7.3', '7.4']
+
+            fail-fast: false
+
+        name: PHP ${{ matrix.php }} tests
+        steps:
+            - uses: actions/checkout@v2
+            - uses: shivammathur/setup-php@v1
+              with:
+                  php-version: ${{ matrix.php }}
+                  extensions: json, mbstring, xml, tokenizer
+                  coverage: none
+
+            - run: mkdir -p tests/tmp
+            - run: cat $(php -r 'echo php_ini_loaded_file() . " " . str_replace("\n", " ", str_replace(",", "", php_ini_scanned_files()));') > tests/tmp/php.ino
+            - run: composer install --no-interaction --prefer-source
+            - run: vendor/bin/tester tests -s -C
+            - if: failure()
+              uses: actions/upload-artifact@v1
+              with:
+                  name: output
+                  path: tests/PdfResponse/output
+
+    lowest_dependencies:
+        name: Lowest Dependencies
+        runs-on: ubuntu-latest
+        steps:
+            - uses: actions/checkout@v2
+            - uses: shivammathur/setup-php@v1
+              with:
+                  php-version: 7.1
+                  extensions: json, mbstring, xml, tokenizer
+                  coverage: none
+
+            - run: mkdir -p tests/tmp
+            - run: cat $(php -r 'echo php_ini_loaded_file() . " " . str_replace("\n", " ", str_replace(",", "", php_ini_scanned_files()));') > tests/tmp/php.ino
+            - run: composer update --no-interaction --prefer-dist --prefer-lowest --prefer-stable
+            - run: vendor/bin/tester tests -s -C
+
+
+    code_coverage:
+        name: Code Coverage
+        runs-on: ubuntu-latest
+        steps:
+            - uses: actions/checkout@v2
+            - uses: shivammathur/setup-php@v1
+              with:
+                  php-version: 7.4
+                  extensions: json, mbstring, xml, tokenizer
+                  coverage: none
+
+            - run: mkdir -p tests/tmp
+            - run: cat $(php -r 'echo php_ini_loaded_file() . " " . str_replace("\n", " ", str_replace(",", "", php_ini_scanned_files()));') > tests/tmp/php.ino
+            - run: composer install --no-progress --prefer-dist
+            - run: wget https://github.com/satooshi/php-coveralls/releases/download/v1.0.1/coveralls.phar
+            - run: vendor/bin/tester -p phpdbg tests -s -c tests/tmp/php.ino --coverage ./coverage.xml --coverage-src ./src
+            - run: php coveralls.phar --verbose --config tests/.coveralls.yml

tests/.coveralls.yml

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+# for php-coveralls
+service_name: travis-ci
+coverage_clover: coverage.xml
+json_path: coverage.json