Add shoulda-matchers and begin using

Gemfile

@@ -70,6 +70,7 @@ group :development, :ci, :test do
   gem 'rubocop-rails', '~> 2.9'
   gem 'rubocop-rake', '~> 0.5.1'
   gem 'rubocop-rspec', '~> 2.2'
+  gem 'shoulda-matchers', '~> 5.0.0'
 end
 
 group :ci, :test do

Gemfile.lock

@@ -364,6 +364,8 @@ GEM
       sprockets-rails
       tilt
     semantic_range (3.0.0)
+    shoulda-matchers (5.0.0)
+      activesupport (>= 5.2.0)
     sixarm_ruby_unaccent (1.2.0)
     sprockets (3.7.2)
       concurrent-ruby (~> 1.0)
@@ -465,6 +467,7 @@ DEPENDENCIES
   rubocop-rspec (~> 2.2)
   sassc (~> 2.0, >= 2.0.1)
   sassc-rails (~> 2.1, >= 2.1.2)
+  shoulda-matchers (~> 5.0.0)
   sprockets (~> 3.7)
   stripe (~> 1.58)
   stripe-ruby-mock (~> 2.4.1)!

NOTICE-ruby

@@ -2591,6 +2591,35 @@ OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 
+------
+
+** shoulda-matchers; version 5.0.0 -- 
+Copyright/License ( copyright-license) About
+
+Copyright (c) 2006-2021 Tammer Saleh and thoughtbot, inc.
+
+Permission is hereby granted, free of charge, to any person
+obtaining a copy of this software and associated documentation
+files (the "Software"), to deal in the Software without
+restriction, including without limitation the rights to use,
+copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the
+Software is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+OTHER DEALINGS IN THE SOFTWARE.
+
+
 ------
 
 ** rack-proxy; version 0.6.5 -- 

spec/models/transaction_spec.rb

@@ -7,6 +7,10 @@ require 'rails_helper'
 RSpec.describe Transaction, type: :model do
   include_context :shared_donation_charge_context
   
+  describe 'validation' do
+    it {is_expected.to validate_presence_of(:supporter)}
+  end
+
   describe 'to_builder' do 
     subject { supporter.transactions.create(
         amount: 1000,

spec/rails_helper.rb

@@ -74,4 +74,11 @@ RSpec.configure do |config|
   config.include Devise::Test::ControllerHelpers, type: :controller
   config.include Devise::Test::IntegrationHelpers, type: :request
   config.include RSpec::Rails::RequestExampleGroup, type: :request, file_path: %r{spec/api}
+
+  Shoulda::Matchers.configure do |config|
+    config.integrate do |with|
+      with.test_framework :rspec
+      with.library :rails
+    end
+  end  
 end