Extract zip and check content

This commit improves the test coverage by extracting the zip and
asserting the number of entries.

Gemfile

@@ -6,6 +6,7 @@ group :development, :test do
   gem 'rake', '~> 13.0.1'
   gem 'pry-byebug'
   gem 'rubocop', '~> 0.66.0'
+  gem 'rubyzip', '~> 2.3.2'
 end
 
 gem "faraday-follow_redirects", "~> 0.3.0"

spec/integrations/workflow_run_spec.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require_relative '../shared_contexts/with_workflow_run'
+require 'zip'
 
 describe Onfido::WorkflowRun do
   describe 'Workflow run' do
@@ -80,10 +81,12 @@
         expect(file.size).to be > 0
       end
 
-      it 'downloads evidence folder' do
+      it 'downloads an evidence folder' do
         file = onfido_api.download_evidence_folder(workflow_run_id)
 
-        expect(file.size).to be > 0
+        Zip::File.open(file.path) do |zip|
+          expect(zip.entries.size).to be > 0
+        end
       end
     end
   end