[#29] Throw error if selenium is not running.

Checklist before requesting a review

closes #29

[x] I have formatted the subject to include ticket number as [#123] Verb in past tense with dot at the end.
[x] I have added a link to the issue tracker
[x] I have provided information in Changed section about WHY something was done if this was not a normal implementation
[x] I have performed a self-review of my code
[x] I have commented my code, particularly in hard-to-understand areas
[x] I have added tests that prove my fix is effective or that my feature works
[x] I have run new and existing relevant tests locally with my changes, and they passed
[x] I have provided screenshots, where applicable