forgot b.bed in coverage unit tests

test/coverage/b.bed

+chr1	0	75	19	75	+
+chr1	3	78	15	75	+
+chr1	74	149	7	75	+
+chr1	77	152	16	75	-
+chr1	92	167	6	75	+
+chr1	116	191	9	75	+
+chr1	128	203	12	75	-
+chr1	132	207	10	75	-
+chr1	143	218	20	75	-
+chr1	163	238	8	75	-
+chr2	6	81	17	75	-
+chr2	39	114	4	75	+
+chr2	74	149	11	75	-
+chr2	77	152	1	75	+
+chr2	114	189	3	75	-
+chr2	127	202	5	75	-
+chr2	131	206	13	75	+
+chr2	137	212	2	75	-
+chr2	139	214	18	75	-
+chr2	163	238	14	75	+