True when filter selects fullName, using QUnit's semantics:

• /re/ or /re/i — regex (case-SENSITIVE without the i flag)
• anything else — case-INSENSITIVE substring
• a leading ! inverts either form

An empty/absent filter matches everything, mirroring QUnit's if (filter) guard.

matchQUnitFilter('cart', 'Cart: adds an item'); // true — case-insensitive substring
matchQUnitFilter('!cart', 'Cart: adds an item'); // false — a leading ! inverts
matchQUnitFilter('/^cart/', 'Cart: adds an item'); // false — regexes are case-SENSITIVE
matchQUnitFilter('/^cart/i', 'Cart: adds an item'); // true
matchQUnitFilter(undefined, 'Cart: adds an item'); // true — no filter matches everything