added phpunit.xml

phpunit.xml

+<phpunit bootstrap="vendor/autoload.php"
+         colors="true"
+         convertErrorsToExceptions="true"
+         convertNoticesToExceptions="false"
+         convertWarningsToExceptions="true"
+         stopOnFailure="false">
+    <testsuites>
+        <testsuite name="Unit Tests">
+            <directory>tests</directory>
+        </testsuite>
+    </testsuites>
+    <filter>
+        <whitelist processUncoveredFilesFromWhitelist="true">
+            <directory suffix=".php">src</directory>
+            <exclude>
+                <directory suffix=".php">vendor</directory>
+            </exclude>
+        </whitelist>
+    </filter>
+</phpunit>