Refine expect_rejection assertions

spec/support/helpers/rack_attack_spec_helpers.rb

@@ -26,18 +26,35 @@ module RackAttackSpecHelpers
     { 'AUTHORIZATION' => "Basic #{encoded_login}" }
   end
 
+  # rubocop:disable Metrics/AbcSize
   def expect_rejection(&block)
     yield
 
     expect(response).to have_gitlab_http_status(:too_many_requests)
     expect(response).to have_header('Retry-After')
+    expect(response.headers['Retry-After']).to match(/^\d+$/)
+
     expect(response).to have_header('RateLimit-Limit')
+    expect(response.headers['RateLimit-Limit']).to match(/^\d+$/)
+
     expect(response).to have_header('RateLimit-Observed')
+    expect(response.headers['RateLimit-Observed']).to match(/^\d+$/)
+
     expect(response).to have_header('RateLimit-Remaining')
+    expect(response.headers['RateLimit-Remaining']).to match(/^\d+$/)
+
     expect(response).to have_header('RateLimit-Reset')
+    expect(response.headers['RateLimit-Reset']).to match(/^\d+$/)
+
     expect(response).to have_header('RateLimit-ResetTime')
+    expect do
+      Time.httpdate(response.headers['RateLimit-ResetTime'])
+    end.not_to raise_error
+
     expect(response).to have_header('Retry-After')
+    expect(response.headers['Retry-After']).to match(/^\d+$/)
   end
+  # rubocop:enable Metrics/AbcSize
 
   def expect_ok(&block)
     yield