Add a test for the partial being rendered

spec/fixtures/forms/2021_2022.json

@@ -367,6 +367,7 @@
                   "earnings": {
                     "check_answer_label": "Income",
                     "header": "What is the tenant’s /and partner’s combined income after tax?",
+                    "guidance_partial": "what_counts_as_income",
                     "type": "numeric",
                     "min": 0,
                     "step": 1,

spec/requests/form_controller_spec.rb

@@ -66,6 +66,13 @@ RSpec.describe FormController, type: :request do
             expect(response).to have_http_status(:not_found)
           end
         end
+
+        context "a form page that has custom guidance" do
+          it "displays the correct partial" do
+            get "/logs/#{case_log.id}/net-income", headers: headers, params: {}
+            expect(response.body).to match("What counts as income?")
+          end
+        end
       end
 
       context "check answers pages" do