Add and improve test coverage

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

@@ -0,0 +1,60 @@
+<?php
+
+namespace Box\Spout\Reader\Helper\XLSX;
+
+/**
+ * Class CellHelperTest
+ *
+ * @package Box\Spout\Reader\Helper\XLSX
+ */
+class CellHelperTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @return void
+     */
+    public function testFillMissingArrayIndexes()
+    {
+        $arrayToFill = [1 => 1, 3 => 3];
+        $filledArray = CellHelper::fillMissingArrayIndexes($arrayToFill, 'FILL');
+
+        $expectedFilledArray = ['FILL', 1, 'FILL', 3];
+        $this->assertEquals($expectedFilledArray, $filledArray);
+    }
+
+    /**
+     * @return array
+     */
+    public function dataProviderForTestGetColumnIndexFromCellIndex()
+    {
+        return [
+            ['A1', 0],
+            ['Z3', 25],
+            ['AA5', 26],
+            ['AB24', 27],
+            ['BC5', 54],
+            ['BCZ99', 1455],
+        ];
+    }
+
+    /**
+     * @dataProvider dataProviderForTestGetColumnIndexFromCellIndex
+     *
+     * @param string $cellIndex
+     * @param int $expectedColumnIndex
+     * @return void
+     */
+    public function testGetColumnIndexFromCellIndex($cellIndex, $expectedColumnIndex)
+    {
+        $this->assertEquals($expectedColumnIndex, CellHelper::getColumnIndexFromCellIndex($cellIndex));
+    }
+
+    /**
+     * @expectedException \Box\Spout\Common\Exception\InvalidArgumentException
+     *
+     * @return void
+     */
+    public function testGetColumnIndexFromCellIndexShouldThrowIfInvalidCellIndex()
+    {
+        CellHelper::getColumnIndexFromCellIndex('InvalidCellIndex');
+    }
+}