Support PHPUnit 6

tests/Spout/Reader/XLSX/Helper/CellHelperTest.php

@@ -3,11 +3,12 @@
 namespace Box\Spout\Reader\XLSX\Helper;
 
 use Box\Spout\Common\Exception\InvalidArgumentException;
+use PHPUnit\Framework\TestCase;
 
 /**
  * Class CellHelperTest
  */
-class CellHelperTest extends \PHPUnit_Framework_TestCase
+class CellHelperTest extends TestCase
 {
     /**
      * @return array

tests/Spout/Reader/XLSX/Helper/CellValueFormatterTest.php

@@ -5,11 +5,12 @@ namespace Box\Spout\Reader\XLSX\Helper;
 use Box\Spout\Common\Helper\Escaper;
 use Box\Spout\Reader\Exception\InvalidValueException;
 use Box\Spout\Reader\XLSX\Manager\StyleManager;
+use PHPUnit\Framework\TestCase;
 
 /**
  * Class CellValueFormatterTest
  */
-class CellValueFormatterTest extends \PHPUnit_Framework_TestCase
+class CellValueFormatterTest extends TestCase
 {
     /**
      * @return array

tests/Spout/Reader/XLSX/Helper/DateFormatHelperTest.php

@@ -2,10 +2,12 @@
 
 namespace Box\Spout\Reader\XLSX\Helper;
 
+use PHPUnit\Framework\TestCase;
+
 /**
  * Class DateFormatHelperTest
  */
-class DateFormatHelperTest extends \PHPUnit_Framework_TestCase
+class DateFormatHelperTest extends TestCase
 {
     /**
      * @return array