identifiable error on cache miss

refs CNVS-26368

make sure we can find instances where we're unable to find accounts
by throwing a specific error (rather than counting on
ActiveRecord::RecordNotFound) for that case.

TEST PLAN:
 1) we should start seeing AccountCacheErrors showing up in Sentry

Change-Id: I9ae05df6a7ac2ca921ace70f10eeae32f11b2e70
Reviewed-on: https://gerrit.instructure.com/70468
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins
Product-Review: Ethan Vizitei <evizitei@instructure.com>
QA-Review: Ethan Vizitei <evizitei@instructure.com>

Author: evizitei

app/models/account.rb

@@ -1101,11 +1101,17 @@ def self.#{key}(force_create = false)
   def precache
   end
 
+  class ::Canvas::AccountCacheError < StandardError; end
+
   def self.find_cached(id)
     birth_id = Shard.relative_id_for(id, Shard.current, Shard.birth)
     Shard.birth.activate do
       Rails.cache.fetch(account_lookup_cache_key(birth_id)) do
-        account = Account.find(birth_id)
+        begin
+          account = Account.find(birth_id)
+        rescue ActiveRecord::RecordNotFound => e
+          raise ::Canvas::AccountCacheError, e.message
+        end
         account.precache
         account
       end
@@ -1119,7 +1125,7 @@ def self.get_special_account(special_account_type, default_account_name, force_c
         special_account_id = special_account_ids[special_account_type] ||= Setting.get("#{special_account_type}_account_id", nil)
         begin
           account = special_accounts[special_account_type] = Account.find_cached(special_account_id) if special_account_id
-        rescue ActiveRecord::RecordNotFound
+        rescue ::Canvas::AccountCacheError
           raise unless Rails.env.test?
         end
       end

spec/models/account_spec.rb

@@ -1408,6 +1408,8 @@ def account_with_admin_and_restricted_user(account, restricted_role)
     specs_require_sharding
 
     describe ".find_cached" do
+      let(:nonsense_id){ 987654321 }
+
       it "works relative to a different shard" do
         @shard1.activate do
           a = Account.create!
@@ -1416,8 +1418,15 @@ def account_with_admin_and_restricted_user(account, restricted_role)
       end
 
       it "errors if infrastructure fails and we can't see the account" do
-        nonsense_id = 987654321
-        expect{ Account.find_cached(nonsense_id) }.to raise_error(ActiveRecord::RecordNotFound)
+        expect{ Account.find_cached(nonsense_id) }.to raise_error(::Canvas::AccountCacheError)
+      end
+
+      it "includes the account id in the error message" do
+        begin
+          Account.find_cached(nonsense_id)
+        rescue ::Canvas::AccountCacheError => e
+          expect(e.message).to eq("Couldn't find Account with id=#{nonsense_id}")
+        end
       end
     end