How do I test changes made to the repo while fixing an issue?

I am trying to fix an open issue in the MeteorJs repo on github. I built the development environment like the repo said and cloned the repo like this-

I have looked at the issue and made the necessary change that may fix the issue. But how do I test that the issue has been fixed? I have made a change to the code of the MeteorJs environment but how do I check if the issue is being handled through my change. If I build the meteorJS environment normally would’nt that be built without my change in it.

In conclusion what I want to know is that if we make changes to the repos of frameworks and environments to fix issues in them, how can we test our changes as if we run the frameworks normally they won’t have the changes we make.

When running meteor run, use meteor from where you cloned the repo

/path/where/you/cloned/meteor run

I checked, and it is indicated in