Trouble creating pivot table without aggregate function

[levers]

I have a view with two dimensions (serial_number and condition) and a measure (test_metric) of type: number. The data for these is from a table already in my database (my_table). In an explore I’d like to pivot on condition so that each distinct value of condition ultimately gets plotted as a different series. However I keep getting the following error:

ERROR: column "test_metric" must appear in the GROUP BY clause or be used in an aggregate function.

view: test_results {
  sql_table_name: public.my_table;;

    dimension: serial_number {
      type: number
      sql: ${TABLE}.serial_number ;;
    }

    dimension: condition {
      type: string
      sql: ${TABLE}.condition ;;
    }

    measure: test_metric {
      type: number
      sql: ${TABLE}.test_metric ;;
    }
}

I’ve looked up this error and there appear to be a few answers but I’m having difficulty implementing them or they don’t seem applicable. For instance if it’s as simple as adding test_metric to the GROUP BY clause, how do I do that in lookml?

This seems like a really straight forward implementation where I want to plot data as is and not use an aggregate measure. 

Thanks in advance.