Use os.replace instead of os.remove; remove a "no cover"

nilmdb/utils/atomic.py

@@ -4,8 +4,7 @@ import os
 
 def replace_file(filename, content):
     """Attempt to atomically and durably replace the filename with the
-    given contents.  This is intended to be 'pretty good on most
-    OSes', but not necessarily bulletproof."""
+    given contents"""
 
     newfilename = filename + b".new"
 
@@ -16,11 +15,4 @@ def replace_file(filename, content):
         os.fsync(f.fileno())
 
     # Move new file over old one
-    try:
-        os.rename(newfilename, filename)
-    except OSError: # pragma: no cover
-        # Some OSes might not support renaming over an existing file.
-        # This is definitely NOT atomic!
-        os.remove(filename)
-        os.rename(newfilename, filename)
-
+    os.replace(newfilename, filename)

tests/test_misc.py

@@ -32,3 +32,15 @@ class TestMisc(object):
                 return None
         with assert_raises(TypeError):
             nilmdb.utils.lock.exclusive_lock(FakeFile())
+
+    def test_replace_file(self):
+        fn = b"tests/misc-testdb/file"
+        try:
+            os.mkdir(os.path.dirname(fn))
+        except FileExistsError:
+            pass
+        with open(fn, "wb") as f:
+            f.write(b"hello, world")
+        nilmdb.utils.atomic.replace_file(fn, b"goodbye, world")
+        with open(fn, "rb") as f:
+            eq_(f.read(), b"goodbye, world")