class Sequel::Mock::Dataset

def columns(*cs)

default Sequel behavior and return the columns.
for this dataset and return self. Otherwise, use the
If arguments are provided, use them to set the columns 
def columns(*cs)
  if cs.empty?
    super
  else
    @columns = cs
    self
  end
end

def execute(sql, opts={}, &block) 

def execute(sql, opts={}, &block)
  super(sql, opts.merge(:dataset=>self), &block)
end

def execute_dui(sql, opts={}, &block) 

def execute_dui(sql, opts={}, &block)
  super(sql, opts.merge(:dataset=>self), &block)
end

def execute_insert(sql, opts={}, &block) 

def execute_insert(sql, opts={}, &block)
  super(sql, opts.merge(:dataset=>self), &block)
end

def fetch_rows(sql, &block) 

def fetch_rows(sql, &block)
  execute(sql, &block)
end