check bytes written in dcd directly

Author: kain88-de

testsuite/MDAnalysisTests/formats/test_libdcd.py

@@ -242,6 +242,24 @@ def test_write_header(tmpdir):
         assert header['nsavc'] == 10
         assert np.allclose(header['delta'], .02)
 
+    # we also check the bytes written directly
+
+    with open(testfile, 'br') as fh:
+        header_bytes = fh.read()
+
+    # check for magic number
+    assert int.from_bytes(header_bytes[:4], byteorder='little') == 84
+    # magic number should be written again before remark section
+    assert int.from_bytes(header_bytes[88:92], byteorder='little') == 84
+    # length of remark section. We hard code this to 244 right now
+    assert int.from_bytes(header_bytes[92:96], byteorder='little') == 244
+    # say we have 3 block of length 80
+    assert int.from_bytes(header_bytes[96:100], byteorder='little') == 3
+    # after the remark section the length should be reported again
+    assert int.from_bytes(header_bytes[340:344], byteorder='little') == 244
+    # this is a magic number as far as I see
+    assert int.from_bytes(header_bytes[344:348], byteorder='little') == 4
+
 
 def test_write_no_header(tmpdir):
     fname = str(tmpdir.join('test.dcd'))