Add test cases for payments and currency service

[dineshnagarit]

There should be unit test cases for payments and currency microserivce.

[ahmetb]

We have limited test cases in most microservices, mostly because it’s a demo app.
However if you can contribute some, and make them part of the build process (probably the Dockerfile?) it’d be appreciated.

[dineshnagarit]

@ahmetb I am planing to work on this next week, I will keep you updated about the progress.

[daniel-sanche]

We're closing this and other kind/improvement issues as we attempt to move the project into a stable maintenance state. Let me know if still plan on working on this and I can re-open