I\'d like to do the following but can\'t due to the nature of fill_in expecting a locator as the first argument.
find(:css, \"input[id$=\'donation_pledge_hun
If you have a reference to the element itself you'd use set instead of fill_in:
set
fill_in
find(:css, "input[id$='donation_pledge_hundreds']").set("10")
However for your specific example, fill_in should be able to find the element as you know it's ID:
fill_in 'donation_pledge_hundreds', with: "10"