Test/show diff for new cels

.travis.yml

@@ -0,0 +1,22 @@
+dist: bionic
+sudo: required
+
+language: php
+
+php:
+  - 7.4.28
+
+install:
+  - composer validate --no-check-all --no-check-publish
+  - composer install
+
+script: ./vendor/bin/phpunit testbench/xlsxwriter.class.Test.php
+
+after_success:
+  - bash <(curl -s https://codecov.io/bash)
+
+cache:
+  apt: true
+  directories:
+    - $TRAVIS_BUILD_DIR/vendor
+    - $HOME/.composer/cache

composer.json

@@ -10,6 +10,6 @@
         "classmap": ["xlsxwriter.class.php"]
     },
     "require-dev": {
-        "phpunit/phpunit": "4.3.*"
+        "phpunit/phpunit": "^7.5"
     }
 }