Create a temporary staging table for a CharlieCard CSV import, with a card code, station name, fare and tap time. Make the fare numeric with a check that it isn't negative, and make the other required columns NOT NULL. Then add a source column that defaults to csv, and insert two rows of your own with INSERT ... VALUES.
The table stays temporary. Return the two rows you loaded, with their source.
Expected: 2 rows, both with source = 'csv', numeric fares and timestamptz tap times. The table is gone once the connection ends.