Add unit tests for FileUpload Vulnerability

[preetkaran20]

Is your feature request related to a problem? Please describe.
We are looking at increasing the Test coverage for the project for its stability so this task is to add junit tests for https://github.com/SasanLabs/VulnerableApp/tree/master/src/main/java/org/sasanlabs/service/vulnerability/fileupload

[preetkaran20]

Parent issue: #212

[shlokam]

@preetkaran20 Can you assign this issue to me?

[shlokam]

@preetkaran20 For the purpose of testing, I need to update a thing. For that should I add a new dependency or can I add some code to the existing source code?

[preetkaran20]

@shlokam as you wish, please raise the PR and we will discuss on that. However, which library you are looking to add and what does it helps in?