**Is your feature request related to a problem?/Why is this needed** <!-- A clear and concise description of what the problem is. Ex. I'm always frustrated when [...] --> **Describe the solution you'd like in detail** <!-- A clear and concise description of what you want to happen. --> Current ut coverage is 78%, details: https://coveralls.io/github/kubernetes-sigs/azurefile-csi-driver?branch=master  **Describe alternatives you've considered** <!-- A clear and concise description of any alternative solutions or features you've considered. --> target num: 85% **Additional context** <!-- Add any other context or screenshots about the feature request here. -->