Adding dev dependencies and travis file.

.travis.yml

+language: php
+
+branches:
+  # Only test the master branch and SemVer tags.
+  only:
+    - master
+    - /^[[:digit:]]+\.[[:digit:]]+\.[[:digit:]]+.*$/
+
+php:
+  - 7.4
+
+matrix:
+  fast_finish: true
+
+cache:
+  apt: true
+  directories:
+    - "$HOME/.composer/cache"
+    - "vendor"
+
+install:
+  - composer install
+
+before_script:
+  # Additional PHP config
+  - phpenv config-add travis.php.ini
+
+script:
+  - composer test

composer.json

@@ -12,10 +12,37 @@
     "minimum-stability": "beta",
     "prefer-stable": true,
     "require": {
+        "php": ">=7.3",
         "guzzlehttp/guzzle": "^6",
         "composer/semver": "^3.2",
         "kevinrob/guzzle-cache-middleware": "^3.3",
         "doctrine/cache": "^1.10",
         "doctrine/common": "^3.1"
+    },
+    "config": {
+        "optimize-autoloader": true,
+        "sort-packages": true
+    },
+    "scripts": {
+        "cs": "phpcs -n --standard=PSR2 src --exclude=Generic.Files.LineLength",
+        "cbf": "phpcbf -n --standard=PSR2 src --exclude=Generic.Files.LineLength",
+        "unit": "phpunit",
+        "lint": [
+            "find src -name '*.php' -print0 | xargs -0 -n1 php -l"
+        ],
+        "test": [
+            "@lint",
+            "@cs"
+        ]
+    },
+    "extra": {
+        "branch-alias": {
+            "dev-master": "1.x-dev"
+        }
+    },
+    "require-dev": {
+        "dealerdirect/phpcodesniffer-composer-installer": "^0.7.1",
+        "drupal/coder": "^8.3",
+        "phpunit/phpunit": "^9.5"
     }
 }