Improved PHPUnit configuration.

.gitignore

 vendor/*
+/.phpunit.result.cache

composer.json

@@ -27,7 +27,7 @@
     "squizlabs/php_codesniffer": "^3.5"
   },
   "scripts": {
-    "test": "phpunit --bootstrap=vendor/autoload.php --color=always --testdox tests/",
+    "test": "phpunit  --coverage-text --colors=always --testdox",
     "cs-check": "phpcs",
     "cs-fix": "phpcbf"
   }

phpunit.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
+         bootstrap="vendor/autoload.php">
+    <testsuites>
+        <testsuite name="stack-logger">
+            <directory>./tests</directory>
+        </testsuite>
+    </testsuites>
+
+    <coverage processUncoveredFiles="true">
+        <include>
+            <directory suffix=".php">src</directory>
+        </include>
+    </coverage>
+</phpunit>