Ensure the #max_allowed_packet method exists for the MysqlAdapters.

https://github.com/zdennis/activerecord-import/issues#issue/12

lib/activerecord-import/adapters/mysql_adapter.rb

@@ -6,7 +6,16 @@ module ActiveRecord::Import::MysqlAdapter
         include ActiveRecord::Import::OnDuplicateKeyUpdateSupport
       end
     end
-  
+    
+    # Returns the maximum number of bytes that the server will allow
+    # in a single packet
+    def max_allowed_packet # :nodoc:
+      result = execute( "SHOW VARIABLES like 'max_allowed_packet';" )
+      # original Mysql gem responds to #fetch_row while Mysql2 responds to #first
+      val = result.respond_to?(:fetch_row) ? result.fetch_row[1] : result.first[1]
+      val.to_i
+    end
+    
     # Returns a generated ON DUPLICATE KEY UPDATE statement given the passed
     # in +args+. 
     def sql_for_on_duplicate_key_update( table_name, *args ) # :nodoc:

test/support/mysql/import_examples.rb

@@ -1,4 +1,32 @@
 def should_support_mysql_import_functionality
+
+  describe "building insert value sets" do
+    it "should properly build insert value set based on max packet allowed" do
+      values = [
+        "('1','2','3')",
+        "('4','5','6')",
+        "('7','8','9')" ]
+      
+      adapter = ActiveRecord::Base.connection.class
+      values_size_in_bytes = adapter.sum_sizes( *values )
+      base_sql_size_in_bytes = 15
+      max_bytes = 30
+    
+      value_sets = adapter.get_insert_value_sets( values, base_sql_size_in_bytes, max_bytes )
+      assert_equal 3, value_sets.size, 'Three value sets were expected!'
+     
+      # Each element in the value_sets array must be an array
+      value_sets.each_with_index { |e,i| 
+        assert_kind_of Array, e, "Element #{i} was expected to be an Array!" }
+
+      # Each element in the values array should have a 1:1 correlation to the elements
+      # in the returned value_sets arrays
+      assert_equal values[0], value_sets[0].first
+      assert_equal values[1], value_sets[1].first
+      assert_equal values[2], value_sets[2].first
+    end
+  end
+
   describe "#import with :on_duplicate_key_update option (mysql specific functionality)" do
     extend ActiveSupport::TestCase::MySQLAssertions