IdentityMap - misc fixes

- Added IdentityMap to be included into AR::Base
- Fixed bug with Mysql namespace missing when running tests only for sqlite
- Added sqlite as default connection

activerecord/lib/active_record/base.rb

@@ -1848,6 +1848,7 @@ def populate_with_current_scope_attributes
     include ActiveModel::MassAssignmentSecurity
     include Callbacks, ActiveModel::Observing, Timestamp
     include Associations, AssociationPreload, NamedScope
+    include IdentityMap
 
     # AutosaveAssociation needs to be included before Transactions, because we want
     # #save_with_autosave_associations to be wrapped inside a transaction.

activerecord/lib/active_record/fixtures.rb

@@ -892,7 +892,9 @@ def setup_fixture_accessors(table_names = nil)
               @fixture_cache[table_name].delete(fixture) if force_reload
 
               if @loaded_fixtures[table_name][fixture.to_s]
-                @fixture_cache[table_name][fixture] ||= @loaded_fixtures[table_name][fixture.to_s].find
+                ActiveRecord::IdentityMap.without do
+                  @fixture_cache[table_name][fixture] ||= @loaded_fixtures[table_name][fixture.to_s].find
+                end
               else
                 raise StandardError, "No fixture with name '#{fixture}' found for table '#{table_name}'"
               end

activerecord/test/cases/adapters/mysql/connection_test.rb

@@ -102,7 +102,7 @@ def test_exec_typecasts_bind_vals
   end
 
   # Test that MySQL allows multiple results for stored procedures
-  if Mysql.const_defined?(:CLIENT_MULTI_RESULTS)
+  if defined?(Mysql) && Mysql.const_defined?(:CLIENT_MULTI_RESULTS)
     def test_multi_results
       rows = ActiveRecord::Base.connection.select_rows('CALL ten();')
       assert_equal 10, rows[0][0].to_i, "ten() did not return 10 as expected: #{rows.inspect}"

activerecord/test/cases/helper.rb

@@ -11,7 +11,14 @@
 
 require 'active_record'
 require 'active_support/dependencies'
-require 'connection'
+begin
+  require 'connection'
+rescue LoadError
+  # If we cannot load connection we assume that driver was not loaded for this test case, so we load sqlite3 as default one.
+  # This allows for running separate test cases by simply running test file.
+  connection_type = defined?(JRUBY_VERSION) ? 'jdbc' : 'native'
+  require "test/connections/#{connection_type}_sqlite3/connection"
+end
 
 begin
   require 'ruby-debug'