code: func NewContext() *Context {
  	ctx, cancel := context.WithCancel(context.Background())
  	sctx := &Context{
  		values:      make(map[fmt.Stringer]interface{}),
  		sessionVars: variable.NewSessionVars(),
  		ctx:         ctx,
  		cancel:      cancel,
  	}
  	sctx.sessionVars.InitChunkSize = 2
  	sctx.sessionVars.MaxChunkSize = 32
  	sctx.sessionVars.StmtCtx.TimeZone = time.UTC
  	sctx.sessionVars.GlobalVarsAccessor = variable.NewMockGlobalAccessor()
  	return sctx
  }
docs: // NewContext creates a new mocked sessionctx.Context.