Add unit test cases to achieve full coverage

[jeandek]

Description of changes:
This PR is adding two additional unit test cases to achieve 100% coverage. It also updates the npm test script to calculate coverage.

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[jenirain]

We may also want to add some details in CONTRIBUTING.MD in the ## Testing the code section:
user should do npm install of:
jest
pino
jsonwebtoken
jwk-to-pem
axios

They need these installed or tests will fail. (if you feel that this is overly obvious, it's ok to leave it out)

[jeandek]

We may also want to add some details in CONTRIBUTING.MD in the ## Testing the code section:
user should do npm install of:
jest
pino
jsonwebtoken
jwk-to-pem
axios

They need these installed or tests will fail. (if you feel that this is overly obvious, it's ok to leave it out)

It's fairly obvious to any experience Node.JS developer, but I'll add some setup instructions regardless.

[jenirain]

IntelliJ tells me that at line 13, we should invoke the superclass constructor. I know in Java this is a best practice, but - as you know - I'm not well versed in js. Do we want to add a call to super() at line 13 - before return DATE; ?

[jeandek]

IntelliJ tells me that at line 13, we should invoke the superclass constructor. I know in Java this is a best practice, but - as you know - I'm not well versed in js. Do we want to add a call to super() at line 13 - before return DATE; ?

Good catch, that's a good practice in JS as well.