Removing whitespace from indented heredoc

trim.rb

require 'minitest/autorun'

class String
  def trim
    file, line_num = caller.first.split(":")
    line = File.read(file).split("\n")[line_num.to_i - 1]
    whitespace_num = line[/^[ ]+/].size + 2
    self.gsub(/^ {#{whitespace_num}}/, '')
  end
end

describe "String#trim" do
  it "removes leading whitespace from indented heredoc" do
    trimmed = <<-end.trim
      level 1
        level 2
    end

    trimmed.must_equal "level 1\n  level 2\n"
  end
end