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

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

spec/requests/api/v1/instance_spec.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe 'Instances' do
+  let(:user)    { Fabricate(:user) }
+  let(:token)   { Fabricate(:accessible_access_token, resource_owner_id: user.id) }
+  let(:headers) { { 'Authorization' => "Bearer #{token.token}" } }
+
+  describe 'GET /api/v1/instance' do
+    context 'when not logged in' do
+      it 'returns http success and json' do
+        get api_v1_instance_path
+
+        expect(response)
+          .to have_http_status(200)
+
+        expect(body_as_json)
+          .to be_present
+          .and include(title: 'Mastodon')
+      end
+    end
+
+    context 'when logged in' do
+      it 'returns http success and json' do
+        get api_v1_instance_path, headers: headers
+
+        expect(response)
+          .to have_http_status(200)
+
+        expect(body_as_json)
+          .to be_present
+          .and include(title: 'Mastodon')
+      end
+    end
+  end
+end