--- a
+++ b/tests/data/pdb/4yzm_ring.pdb
@@ -0,0 +1,33 @@
+HEADER    4YZM_PROTEIN
+COMPND    4YZM_PROTEIN
+REMARK    GENERATED BY X-TOOL on Sun Nov 13 13:39:13 2016
+ATOM      1  N   VAL A1079     -20.548  -3.532 -17.962  1.00 39.74           N
+ATOM      2  H   VAL A1079     -19.600  -3.800 -17.629  1.00  0.00           H
+ATOM      3  CA  VAL A1079     -21.703  -3.900 -17.181  1.00 40.23           C
+ATOM      4  C   VAL A1079     -22.430  -2.750 -16.608  1.00 41.04           C
+ATOM      5  O   VAL A1079     -23.627  -2.719 -16.620  1.00 42.28           O
+ATOM      6  CB  VAL A1079     -21.318  -4.765 -16.009  1.00 40.42           C
+ATOM      7  CG1 VAL A1079     -22.538  -5.368 -15.398  1.00 39.84           C
+ATOM      8  CG2 VAL A1079     -20.415  -5.856 -16.480  1.00 40.72           C
+ATOM      9  N   PHE A1080     -21.699  -1.815 -16.065  1.00 41.51           N
+ATOM     10  H   PHE A1080     -20.662  -1.895 -16.069  1.00  0.00           H
+ATOM     11  CA  PHE A1080     -22.325  -0.690 -15.470  1.00 42.16           C
+ATOM     12  C   PHE A1080     -23.098   0.085 -16.479  1.00 40.18           C
+ATOM     13  O   PHE A1080     -24.224   0.396 -16.243  1.00 40.82           O
+ATOM     14  CB  PHE A1080     -21.224   0.171 -14.879  1.00 44.34           C
+ATOM     15  CG  PHE A1080     -21.675   1.502 -14.400  1.00 47.05           C
+ATOM     16  CD1 PHE A1080     -23.553   1.613 -13.364  1.00 47.00           C
+ATOM     17  CD2 PHE A1080     -21.188   2.636 -14.965  1.00 46.27           C
+ATOM     18  CE1 PHE A1080     -22.964   2.833 -12.925  1.00 47.28           C
+ATOM     19  CE2 PHE A1080     -21.595   3.857 -14.526  1.00 46.80           C
+ATOM     20  CZ  PHE A1080     -22.483   3.953 -13.506  1.00 46.27           C
+ATOM     21  N   ILE A1081     -22.489   0.402 -17.604  1.00 37.20           N
+ATOM     22  H   ILE A1081     -21.501   0.109 -17.743  1.00  0.00           H
+ATOM     23  CA  ILE A1081     -23.158   1.148 -18.655  1.00 36.09           C
+ATOM     24  C   ILE A1081     -24.323   0.471 -19.309  1.00 36.24           C
+ATOM     25  O   ILE A1081     -25.279   1.098 -19.626  1.00 36.36           O
+ATOM     26  CB  ILE A1081     -22.193   1.570 -19.754  1.00 34.38           C
+ATOM     27  CG1 ILE A1081     -21.058   2.340 -19.145  1.00 35.31           C
+ATOM     28  CG2 ILE A1081     -22.889   2.440 -20.769  1.00 32.78           C
+ATOM     29  CD1 ILE A1081     -20.190   3.058 -20.128  1.00 34.86           C
+END