Robust unit tests

[sharathkumaranbu]

We need to create robust unit tests for all commands and the functions in Topcoder CLI.

We need to set up mocks for all possible scenarios and test it thoroughly with strong assertions. Every test should have assertion and assertion should be robust enough. E.g. Instead of validating that a response exist, we need to validate what is expected in the response.

[sharathkumaranbu]

Done through #25