I am writing a readme for my GitHub project in the .md format. Is there a way can I test what my readme.md file will look like before committing to GitHub?
Many ways: If you're on a Mac, use Mou.
If you want to test in a browser, you could try StackEdit, as pointed out by @Aaron or Dillinger since Notepag seems to be down now. Personally I use Dillinger since it just works and saves all my documents in my browser's local database.