diff --git a/spec/models/concerns/remotable_spec.rb b/spec/models/concerns/remotable_spec.rb
new file mode 100644
index 0000000000..0b2dad23f0
--- /dev/null
+++ b/spec/models/concerns/remotable_spec.rb
@@ -0,0 +1,205 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe Remotable do
+  class Foo
+    def initialize
+      @attrs = {}
+    end
+
+    def [](arg)
+      @attrs[arg]
+    end
+
+    def []=(arg1, arg2)
+      @attrs[arg1] = arg2
+    end
+
+    def hoge=(arg); end
+
+    def hoge_file_name=(arg); end
+
+    def has_attribute?(arg); end
+
+    def self.attachment_definitions
+      { hoge: nil }
+    end
+  end
+
+  context 'Remotable module is included' do
+    before do
+      class Foo; include Remotable; end
+    end
+
+    let(:attribute_name) { "#{hoge}_remote_url".to_sym }
+    let(:code)           { 200 }
+    let(:file)           { 'filename="foo.txt"' }
+    let(:foo)            { Foo.new }
+    let(:headers)        { { 'content-disposition' => file } }
+    let(:hoge)           { :hoge }
+    let(:url)            { 'https://google.com' }
+
+    let(:request) do
+      stub_request(:get, url)
+        .to_return(status: code, headers: headers)
+    end
+
+    it 'defines a method #hoge_remote_url=' do
+      expect(foo).to respond_to(:hoge_remote_url=)
+    end
+
+    it 'defines a method #reset_hoge!' do
+      expect(foo).to respond_to(:reset_hoge!)
+    end
+
+    describe '#hoge_remote_url' do
+      before do
+        request
+      end
+
+      it 'always returns arg' do
+        [nil, '', [], {}].each do |arg|
+          expect(foo.hoge_remote_url = arg).to be arg
+        end
+      end
+
+      context 'Addressable::URI::InvalidURIError raised' do
+        it 'makes no request' do
+          allow(Addressable::URI).to receive_message_chain(:parse, :normalize)
+            .with(url).with(no_args).and_raise(Addressable::URI::InvalidURIError)
+
+          foo.hoge_remote_url = url
+          expect(request).not_to have_been_requested
+        end
+      end
+
+      context 'scheme is neither http nor https' do
+        let(:url) { 'ftp://google.com' }
+
+        it 'makes no request' do
+          foo.hoge_remote_url = url
+          expect(request).not_to have_been_requested
+        end
+      end
+
+      context 'parsed_url.host is empty' do
+        it 'makes no request' do
+          parsed_url = double(scheme: 'https', host: double(empty?: true))
+          allow(Addressable::URI).to receive_message_chain(:parse, :normalize)
+            .with(url).with(no_args).and_return(parsed_url)
+
+          foo.hoge_remote_url = url
+          expect(request).not_to have_been_requested
+        end
+      end
+
+      context 'foo[attribute_name] == url' do
+        it 'makes no request' do
+          allow(foo).to receive(:[]).with(attribute_name).and_return(url)
+
+          foo.hoge_remote_url = url
+          expect(request).not_to have_been_requested
+        end
+      end
+
+      context "scheme is https, parsed_url.host isn't empty, and foo[attribute_name] != url" do
+        it 'makes a request' do
+          foo.hoge_remote_url = url
+          expect(request).to have_been_requested
+        end
+
+        context 'response.code != 200' do
+          let(:code) { 500 }
+
+          it 'calls not send' do
+            expect(foo).not_to receive(:send).with("#{hoge}=", any_args)
+            expect(foo).not_to receive(:send).with("#{hoge}_file_name=", any_args)
+            foo.hoge_remote_url = url
+          end
+        end
+
+        context 'response.code == 200' do
+          let(:code) { 200 }
+
+          context 'response contains headers["content-disposition"]' do
+            let(:file)      { 'filename="foo.txt"' }
+            let(:headers)   { { 'content-disposition' => file } }
+
+            it 'calls send' do
+              string_io = StringIO.new('')
+              extname   = '.txt'
+              basename  = '0123456789abcdef'
+
+              allow(SecureRandom).to receive(:hex).and_return(basename)
+              allow(StringIO).to receive(:new).with(anything).and_return(string_io)
+
+              expect(foo).to receive(:send).with("#{hoge}=", string_io)
+              expect(foo).to receive(:send).with("#{hoge}_file_name=", basename + extname)
+              foo.hoge_remote_url = url
+            end
+          end
+
+          context 'if has_attribute?' do
+            it 'calls foo[attribute_name] = url' do
+              allow(foo).to receive(:has_attribute?).with(attribute_name).and_return(true)
+              expect(foo).to receive('[]=').with(attribute_name, url)
+              foo.hoge_remote_url = url
+            end
+          end
+
+          context 'unless has_attribute?' do
+            it 'calls not foo[attribute_name] = url' do
+              allow(foo).to receive(:has_attribute?)
+                .with(attribute_name).and_return(false)
+              expect(foo).not_to receive('[]=').with(attribute_name, url)
+              foo.hoge_remote_url = url
+            end
+          end
+        end
+
+        context 'an error raised during the request' do
+          let(:request) { stub_request(:get, url).to_raise(error_class) }
+
+          error_classes = [
+            HTTP::TimeoutError,
+            HTTP::ConnectionError,
+            OpenSSL::SSL::SSLError,
+            Paperclip::Errors::NotIdentifiedByImageMagickError,
+            Addressable::URI::InvalidURIError,
+          ]
+
+          error_classes.each do |error_class|
+            let(:error_class) { error_class }
+
+            it 'calls Rails.logger.debug' do
+              expect(Rails.logger).to receive(:debug).with(/^Error fetching remote #{hoge}: /)
+              foo.hoge_remote_url = url
+            end
+          end
+        end
+      end
+    end
+
+    describe '#reset_hoge!' do
+      context 'if url.blank?' do
+        it 'returns nil, without clearing foo[attribute_name] and calling #hoge_remote_url=' do
+          url = nil
+          expect(foo).not_to receive(:send).with(:hoge_remote_url=, url)
+          foo[attribute_name] = url
+          expect(foo.reset_hoge!).to be_nil
+          expect(foo[attribute_name]).to be_nil
+        end
+      end
+
+      context 'unless url.blank?' do
+        it 'clears foo[attribute_name] and calls #hoge_remote_url=' do
+          foo[attribute_name] = url
+          expect(foo).to receive(:send).with(:hoge_remote_url=, url)
+          foo.reset_hoge!
+          expect(foo[attribute_name]).to be ''
+        end
+      end
+    end
+  end
+end