Convert /instances/* controller specs to request specs (#27988)

Co-authored-by: Claire <claire.github-309c@sitedethib.com>

spec/requests/api/v1/instances/domain_blocks_spec.rb

@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe 'Domain Blocks' do
+  describe 'GET /api/v1/instance/domain_blocks' do
+    around do |example|
+      original = Setting.show_domain_blocks
+      example.run
+      Setting.show_domain_blocks = original
+    end
+
+    before do
+      Fabricate(:domain_block)
+    end
+
+    context 'with domain blocks set to all' do
+      before { Setting.show_domain_blocks = 'all' }
+
+      it 'returns http success' do
+        get api_v1_instance_domain_blocks_path
+
+        expect(response)
+          .to have_http_status(200)
+
+        expect(body_as_json)
+          .to be_present
+          .and(be_an(Array))
+          .and(have_attributes(size: 1))
+      end
+    end
+
+    context 'with domain blocks set to users' do
+      before { Setting.show_domain_blocks = 'users' }
+
+      it 'returns http not found' do
+        get api_v1_instance_domain_blocks_path
+
+        expect(response)
+          .to have_http_status(404)
+      end
+    end
+
+    context 'with domain blocks set to disabled' do
+      before { Setting.show_domain_blocks = 'disabled' }
+
+      it 'returns http not found' do
+        get api_v1_instance_domain_blocks_path
+
+        expect(response)
+          .to have_http_status(404)
+      end
+    end
+  end
+end