Expand test coverage for PrometheusConnect from 64% to 100%#311

Copilot wants to merge 3 commits intomaster4n4nd/prometheus-api-client-python:masterfrom

copilot/refresh-test-cases-prometheusconnect4n4nd/prometheus-api-client-python:copilot/refresh-test-cases-prometheusconnectCopy head branch name to clipboard