Function gather_empty_test_violations

pub fn gather_empty_test_violations<T>(
    selected_items: &[T],
    subject: impl Into<String>,
    selectors: &[Filter],
    is_negated: bool,
    allow_empty_tests: bool,
) -> Vec<EmptyTestViolation>

Produces the defensive violation for a terminal that selected no subjects.

This assertion deliberately judges the subject selection rather than derived evidence such as dependency edges or cycles. A selected item with no relationships is still a non-empty test.