If k was chosen such that u = k/n > 0 is constant in n and if,
additionally to the tail copula, the copula remained constant over
time, it would follow from Corollary 3.3(a) in Bücher and Volgushev
(2013) that Sn weakly converges to {1 − C(u, u)}
1
0 B2(s) ds,
where B denotes a standard Brownian bridge. Since the critical values
of TDC-Test 1 are the quantiles of
1
0 B2(s) ds, we can easily see
that the test rejects too rarely, provided that C(u, u) > 0. Note that
this argument remains valid if the copula is constant over time only
in a neighborhood of (u, u).