refactor: move Postal::DKIMHeader to app/util/dkim_header

spec/lib/postal/dkim_header_spec.rb

@@ -1,34 +0,0 @@
-# frozen_string_literal: true
-
-require "rails_helper"
-
-describe Postal::DKIMHeader do
-  examples = Rails.root.join("spec/examples/dkim_signing/*.msg")
-  Dir[examples].each do |path|
-    contents = File.read(path)
-    frontmatter, email = contents.split(/^---\n/m, 2)
-    frontmatter = YAML.safe_load(frontmatter)
-    email.strip
-    it "works with #{path.split('/').last}" do
-      mocked_time = Time.at(frontmatter["time"].to_i)
-      allow(Time).to receive(:now).and_return(mocked_time)
-
-      domain = instance_double("Domain")
-      allow(domain).to receive(:dkim_status).and_return("OK")
-      allow(domain).to receive(:name).and_return(frontmatter["domain"])
-      allow(domain).to receive(:dkim_key).and_return(OpenSSL::PKey::RSA.new(frontmatter["private_key"]))
-      allow(domain).to receive(:dkim_identifier).and_return(frontmatter["dkim_identifier"])
-
-      expectation = "DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;\r\n" \
-                    "\td=#{frontmatter['domain']};\r\n" \
-                    "\ts=#{frontmatter['dkim_identifier']}; t=#{mocked_time.to_i};\r\n" \
-                    "\tbh=#{frontmatter['bh']};\r\n" \
-                    "\th=#{frontmatter['headers']};\r\n" \
-                    "\tb=#{frontmatter['b'].scan(/.{1,72}/).join("\r\n\t")}"
-
-      header = described_class.new(domain, email)
-
-      expect(header.dkim_header).to eq expectation
-    end
-  end
-end