added tests and fixed leftover array entries

tests/CsvxmlAvailableFieldsTest.php

@@ -0,0 +1,33 @@
+<?PHP
+/**
+ * This script contains tests for the home page.
+ *
+ * @author Joshua Ramon Enslin <joshua@jrenslin.de>
+ */
+declare(strict_types = 1);
+
+use PHPUnit\Framework\TestCase;
+require_once __DIR__ . "/../functions/functions.php";
+
+/**
+ * Test class for the start page.
+ */
+final class CsvxmlAvailableFieldsTest extends TestCase {
+    /**
+     * Test for HTML output.
+     *
+     * @return void
+     */
+    public function testOutput():void {
+
+        $fieldsGetter = new CsvxmlAvailableFields('en');
+        $availableFields = $fieldsGetter->getFields();
+
+        foreach ($availableFields as $type) {
+            foreach ($type as $name => $entry) {
+                self::assertTrue($entry instanceof FieldEntry, $name . " is not a FieldEntry");
+            }
+        }
+
+    }
+}