improve tests to check for existence of extensions method, and skip testing...

improve tests to check for existence of extensions method, and skip testing dumped extensions if they are unsupported by the database

activerecord/test/cases/adapters/postgresql/hstore_test.rb

@@ -36,6 +36,7 @@ def teardown
   end
 
   def test_hstore_included_in_extensions
+    assert @connection.respond_to?(:extensions), "connection should have a list of extensions"
     assert @connection.extensions.include?('hstore'), "extension list should include hstore"
   end
 

activerecord/test/cases/schema_dumper_test.rb

@@ -231,16 +231,15 @@ def test_schema_dump_includes_decimal_options
   end
 
   if current_adapter?(:PostgreSQLAdapter)
-    if ActiveRecord::Base.connection.supports_extensions?
     def test_schema_dump_includes_extensions
       connection = ActiveRecord::Base.connection
+      return skip unless connection.supports_extensions?
       unless connection.extension_enabled?('hstore')
         connection.enable_extension 'hstore'
       end
       output = standard_dump
       assert_match %r{enable_extension "hstore"}, output
     end
-    end
 
     def test_schema_dump_includes_xml_shorthand_definition
       output = standard_dump