Add Test Cases

[bucker]

Based on this document: https://github.com/microsoft/InventorySample/blob/4909ca77355850508b2b5bd8d8fc12c65d59fe77/docs/Architecture/DependencyInjection.md

Unit Testing: DI enables you to replace complex dependencies, such as databases, with mocked implementations of those dependencies. This allows you to completely isolate the code that is being testing.

Using DI without testing is like lack the last push to achieve the goal. It seems to me that the architecture of this project is extremely suitable for unit testing, and so sad that we don't have any.

I'm willing to add some unit test if you like. :)