How do I compare two text files with RSpec?

On a trivial level:

IO.read(file1).should == IO.read(file2)

If you want to do something nicer, you're likely going to need to write a new matcher, something like have_same_content_as defined to check for the above condition. "Up and Running with Custom RSpec Matchers" is a nice tutorial on writing custom matchers.

For others who stumble across this, check the FileUtils#cmp method:

require 'fileutils'
expect(FileUtils.compare_file(file1, file2)).to be_truthy