test_infer_sig_len: test inferring length of signal file with prolog.

If the header file does not specify the signal length, rdrecord should
calculate it from the size of the signal file.  Test that this works
correctly for a signal file with a prolog.

Author: Benjamin Moody

sample-data/a103l-no-len.hea

@@ -0,0 +1,6 @@
+a103l-no-len 3 250
+a103l.mat 16+24 7247/mV 16 0 -171 -27403 0 II
+a103l.mat 16+24 1.052e+04/mV 16 0 9127 -301 0 V
+a103l.mat 16+24 1.253e+04/NU 16 0 6042 -17391 0 PLETH
+#Asystole
+#False alarm

tests/test_record.py

@@ -707,6 +707,12 @@ def test_infer_sig_len(self):
 
         assert record_2.__eq__(record)
 
+        record = wfdb.rdrecord('sample-data/a103l')
+        record_2 = wfdb.rdrecord('sample-data/a103l-no-len')
+        record_2.record_name = record.record_name
+
+        assert record_2.__eq__(record)
+
 
 class TestDownload(unittest.TestCase):
     # Test that we can download records with no "dat" file