Which test set checks the decision boundary?

A room holds at most 10 people. It contains 4 people before an arriving group asks to enter. The whole group must be admitted if everyone fits, including when the room becomes exactly full. Otherwise, the whole group must be rejected.

Group Size is a positive whole number. Each test starts again with 4 people in the room; groups from earlier tests are not still inside.

Which test set checks the largest group that can be admitted and its nearest smaller and larger group sizes, with all expected results correct?

Table 4: Candidate tests for the room-capacity rule; each arrow gives the expected result for one independent input.
Test set Group sizes and expected results
A 9 -> Reject; 10 -> Reject; 11 -> Reject
B 5 -> Admit; 6 -> Admit; 7 -> Reject
C 1 -> Admit; 2 -> Admit; 3 -> Admit
D 5 -> Admit; 6 -> Reject; 7 -> Reject
  1. Test set A
  2. Test set B
  3. Test set C
  4. Test set D