unit test: more closely mimic rpm2cpio behavior when reading past header

tests/test_lib/test_header_sizes.py

@@ -57,10 +57,11 @@ class TestHeaderSizes(unittest.TestCase):
 
             # The following bit uses rpmlib to read the header, which advances the file
             # pointer past it. This is the same approach rpm2cpio uses.
+            ts = rpm.TransactionSet()
+            ts.setVSFlags(rpm._RPMVSF_NOSIGNATURES | rpm._RPMVSF_NODIGESTS | rpm.RPMVSF_NOHDRCHK)
             fd = os.open(fn, os.O_RDONLY)
             try:
-                os.lseek(fd, s_lead + s_sig, 0)  # seek to header start
-                hdr, h_start = rpm.readHeaderFromFD(fd)
+                hdr = ts.hdrFromFdno(fd)
                 p_offset = os.lseek(fd, 0, os.SEEK_CUR)
             finally:
                 os.close(fd)