public function test_is_valid_sheet_index()
{
$workbook = new Workbook('Workbook title');
// All integers
$this->assertTrue($workbook->isValidIndex(0));
$this->assertTrue($workbook->isValidIndex(1));
// Integers given as string
$this->assertTrue($workbook->isValidIndex('1000'));
// No strings
$this->assertFalse($workbook->isValidIndex('invalid'));
// No decimals
$this->assertFalse($workbook->isValidIndex('0.555'));
}
