tests: we should not hit the live endpoint for our tests, we should mock them

As we keep on adding more and more tests, we shouldn't really hit the live CG endpoints for our tests.

We should utilise [nock](https://github.com/nock/nock) and mock the response we expect from the endpoint(s).

This has one limitation, that being if the endpoint changes (structure and/or properties added/removed) the mocked shape will no longer be accurate

Start by locating the tests that call the live CoinGecko endpoints and inspect how the project currently configures its test suite. Use nock to mock the expected endpoint responses, then verify that the tests pass without contacting the live API.

Written by the indexing model from the issue text.