Test Coverage and SQL Logic | Dataford Interview Questions

How would you ensure you have good test coverage when working with SQLLite queries that increment and decrement a score using a WHERE condition?

Use the provided PostgreSQL tables to apply eligible score changes and return the affected scores. Coverage should account for increments, decrements, zero and NULL amounts, disabled changes, invalid operations, missing scores, and NULL current scores.

Output

Return one row per updated score with score_id, new_score, net_change, and applied_change_count.
Include only scores changed by eligible requests.
Order by score_id ascending.

Schema

scores

Column	Type	Description
score_idPK	INT	Unique score record identifier
current_score	INT	Current score value

score_changes

Column	Type	Description
change_idPK	INT	Unique score change identifier
score_id	INT	Referenced score record
operation	VARCHAR(20)	Requested operation
amount	INT	Magnitude of the requested change
applies	BOOLEAN	Whether the request is enabled
created_at	TIMESTAMP	Creation timestamp used for deterministic ordering

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