tests: Update the datagram tests

tests/putil/test_datagram.py

@@ -96,6 +96,24 @@ def test_iterator(datagram_small):
     dgi = core.DatagramIterator(dg)
     verify(dgi)
 
+# This tests the copy constructor:
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+def test_copy(datagram_small):
+    dg, verify = datagram_small
+
+    dg2 = core.Datagram(dg)
+    dgi = core.DatagramIterator(dg2)
+    verify(dgi)
+
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+def test_assign(datagram_small):
+    dg, verify = datagram_small
+
+    dg2 = core.Datagram()
+    dg2.assign(dg)
+    dgi = core.DatagramIterator(dg2)
+    verify(dgi)
+
 
 # These test DatagramInputFile/DatagramOutputFile:
 
@@ -147,10 +165,10 @@ def test_file_corrupt(datagram_small, tmpdir):
     dof.put_datagram(dg)
     dof.close()
 
-    # Corrupt the size header to 4GB
-    with p.open(mode='wb') as f:
+    # Corrupt the size header to 1GB
+    with p.open(mode='r+b') as f:
         f.seek(0)
-        f.write(b'\xFF\xFF\xFF\xFF')
+        f.write(b'\xFF\xFF\xFF\x4F')
 
     dg2 = core.Datagram()
     dif = core.DatagramInputFile()
@@ -158,4 +176,15 @@ def test_file_corrupt(datagram_small, tmpdir):
     assert not dif.get_datagram(dg2)
     dif.close()
 
+    # Truncate the file
+    for size in [12, 8, 4, 3, 2, 1, 0]:
+        with p.open(mode='r+b') as f:
+            f.truncate(size)
+
+        dg2 = core.Datagram()
+        dif = core.DatagramInputFile()
+        dif.open(filename)
+        assert not dif.get_datagram(dg2)
+        dif.close()
+
     # Should we test that dg2 is unmodified?