There are interesting test cases:

    SELECT MIN(C1) FROM T WHERE C1 = ? AND C2 = ?
    SELECT MIN(C2) FROM T WHERE C1 = ? AND C2 = ?

but given that these columns are indexed in both orders, it is difficult to tell whether they would both work if only one index was defined.
Maybe you could try something similar on another table without a reversed index. (Or maybe you already do?)
Add a negative test case: SELECT MIN(C2) FROM T WHERE C1 > ?

Add a (positive?) test case: SELECT MIN(C1) FROM T WHERE C1 = ? AND C2 = ? and