File Reader: does not throw process is using file error

filereader.cs

// DO THIS
using (var filestream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
using (var reader = new StreamReader(filestream))
{
    records = reader.ReadToEnd();
    reader.Close();
}

//// NOT THIS
//using (var reader = new StreamReader(filePath))
//{
//    records = reader.ReadToEnd();
//    reader.Close();
//}