Tests: make sure temporary files are pre-closed

Windows fails with a permission error if the temporary file is already
opened.

Fixes #501

test/test_eds.py

@@ -4,7 +4,7 @@
 import canopen
 from canopen.objectdictionary.eds import _signed_int_from_hex
 from canopen.utils import pretty_index
-from .util import SAMPLE_EDS, DATATYPES_EDS
+from .util import SAMPLE_EDS, DATATYPES_EDS, tmp_file
 
 
 class TestEDS(unittest.TestCase):
@@ -223,10 +223,9 @@ def test_comments(self):
 """.strip())
 
     def test_export_eds_to_file(self):
-        import tempfile
         for suffix in ".eds", ".dcf":
             for implicit in True, False:
-                with tempfile.NamedTemporaryFile(suffix=suffix) as tmp:
+                with tmp_file(suffix=suffix) as tmp:
                     dest = tmp.name
                     doctype = None if implicit else suffix[1:]
                     with self.subTest(dest=dest, doctype=doctype):
@@ -235,9 +234,8 @@ def test_export_eds_to_file(self):
 
     def test_export_eds_to_file_unknown_extension(self):
         import io
-        import tempfile
         for suffix in ".txt", "":
-            with tempfile.NamedTemporaryFile(suffix=suffix) as tmp:
+            with tmp_file(suffix=suffix) as tmp:
                 dest = tmp.name
                 with self.subTest(dest=dest, doctype=None):
                     canopen.export_od(self.od, dest)

test/test_pdo.py

@@ -1,7 +1,7 @@
 import unittest
 
 import canopen
-from .util import SAMPLE_EDS
+from .util import SAMPLE_EDS, tmp_file
 
 
 class TestPDO(unittest.TestCase):
@@ -64,14 +64,13 @@ def test_pdo_save(self):
         self.node.rpdo.save()
 
     def test_pdo_export(self):
-        import tempfile
         try:
             import canmatrix
         except ImportError:
             raise unittest.SkipTest("The PDO export API requires canmatrix")
 
         for pdo in "tpdo", "rpdo":
-            with tempfile.NamedTemporaryFile(suffix=".csv") as tmp:
+            with tmp_file(suffix=".csv") as tmp:
                 fn = tmp.name
                 with self.subTest(filename=fn, pdo=pdo):
                     getattr(self.node, pdo).export(fn)

test/util.py

@@ -1,5 +1,14 @@
+import contextlib
 import os
+import tempfile
 
 
 DATATYPES_EDS = os.path.join(os.path.dirname(__file__), "datatypes.eds")
 SAMPLE_EDS = os.path.join(os.path.dirname(__file__), "sample.eds")
+
+
+@contextlib.contextmanager
+def tmp_file(*args, **kwds):
+    with tempfile.NamedTemporaryFile(*args, **kwds) as tmp:
+        tmp.close()
+        yield tmp