Implement Test Cases

[lvxhnat]

Is your feature request related to a problem? Please describe.
ETF Objects should be tested to ensure that missing fields or ETFs are handled. Currently, some of the fields and the request to ETFDB itself does not handle exceptions such as 404/500 errors gracefully, and has to be caught when calling the object itself.

Describe the solution you'd like
Implemented test cases for the ETF object.

Describe alternatives you've considered

Additional context