user: Question: On which air date was Robert the test-taker?
Columns: ['Air Date', 'Challenge', 'Winner', 'Test-taker', 'Passed?']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['18 April 2007', 'Pace Car Challenge', 'Red', 'N/A', 'N/A']
SQL:

assistant: SELECT "Air Date" FROM "Table" WHERE "Test-taker" = 'Robert';