public async Task AppendAllLinesAsync()
{
if (File.Exists(_filePath))
{
File.Delete(_filePath);
}
File.WriteAllLines(_filePath, _lineContent);
await FileHelper.AppendAllLinesAsync(_filePath, _appendLineContent);
CollectionAssert.AreEqual(_lineContent.Union(_appendLineContent).ToArray(), File.ReadAllLines(_filePath));
File.Delete(_filePath);
}
