Test a unique constraint violation

Prove customers.email rejects an exact duplicate, then expose that the constraint is case-sensitive.

1. 1Insert a customer reusing customer 1's email exactly ('ava.thompson@example.com'); it must fail.
2. 2Insert name 'Ava Upper', email 'AVA.THOMPSON@EXAMPLE.COM', country 'USA', created_at '2025-06-01'; note that it is accepted.
3. 3Report case-insensitive duplicates: SELECT lower(email) AS email, COUNT(*) AS copies FROM customers GROUP BY lower(email) HAVING COUNT(*) > 1.

• The exact duplicate fails with UNIQUE constraint failed
• The last result set reports the case-insensitive duplicate of ava.thompson@example.com

• Every run starts from a freshly seeded database, so your script must include its own setup statements.
• A failing statement is recorded and the script keeps running, so you can trigger an error and verify afterwards.
• Only the last result set of your script is compared, so finish with the verification query.