How do I test a function with gets.chomp in it?

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You could create a pipe and assign its “read end” to $stdin. Writing to the pipe’s “write end” then simulates user input.

Here’s an example with a little helper method with_stdin for setting up the pipe:

require 'test/unit'

class View
  def read_user_input
    gets.chomp
  end
end

class ViewTest < Test::Unit::TestCase
  def test_read_user_input
    with_stdin do |user|
      user.puts "user input"
      assert_equal(View.new.read_user_input, "user input")
    end
  end

  def with_stdin
    stdin = $stdin             # remember $stdin
    $stdin, write = IO.pipe    # create pipe assigning its "read end" to $stdin
    yield write                # pass pipe's "write end" to block
  ensure
    write.close                # close pipe
    $stdin = stdin             # restore $stdin
  end
end

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