Feat/rate limit interface unit test

[shannonlal]

The following is another very simple PR to look at expanding the amount of test coverage. This is linked to issue #36. This PR really focuses on making sure the interfaces have some simple tests. Here is a summary of what was added to the PR:

Changes in PR:

1. Adds a simple spec for the rate-limiter.interface

Outputs

Tests

The following is the output of the tests

npm run test

Linting

npm run lint

Build

npm run build