Adding simple unit test

phpunit.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit backupGlobals="false"
+         backupStaticAttributes="false"
+         bootstrap="vendor/autoload.php"
+         colors="true"
+         convertErrorsToExceptions="true"
+         convertNoticesToExceptions="true"
+         convertWarningsToExceptions="true"
+         processIsolation="false"
+         stopOnFailure="false"
+         syntaxCheck="false"
+>
+    <testsuites>
+        <testsuite name="Htmldiff Tests">
+            <directory>./tests/</directory>
+        </testsuite>
+    </testsuites>
+</phpunit>

tests/HtmldiffTest.php

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+<?php
+
+use Gathercontent\Htmldiff\Htmldiff;
+
+class HtmldiffTest extends PHPUnit_Framework_TestCase
+{
+
+    public function testStringDiff()
+    {
+        $htmldiff = new Htmldiff;
+        $result = $htmldiff->compare("Test", "Testing", true);
+
+        $this->assertEquals("<del>Test</del><ins>Testing</ins>", $result);
+    }
+}