Specify the testsuite directory in phpunit.xml.

This allows phpunit to be run without having to specify the path to the
test suite.  This is a nicety for users and can help make this play well
if we hook it up to scrutinizer.

Author: Spencer Rinehart

build.php

@@ -13,7 +13,7 @@
     exit(1);
 }
 
-passthru('vendor/bin/phpunit --coverage-html coverage --coverage-clover clover.xml tests', $returnStatus);
+passthru('vendor/bin/phpunit --coverage-html coverage --coverage-clover clover.xml', $returnStatus);
 if ($returnStatus !== 0) {
     exit(1);
 }

phpunit.xml

@@ -1,4 +1,7 @@
 <phpunit colors="true" forceCoversAnnotation="true">
+    <testsuite name="Unit Tests">
+        <directory>./tests</directory>
+    </testsuite>
     <filter>
         <whitelist>
             <directory>src</directory>