Fix newlines in config files (c4urself#98)

* Fix newlines in config files

* Update tests which previously expected two blank lines, now expect only one

* Update test_retain_newline to explicitly check for a single newline of the right type at the end of the config

bumpversion/cli.py

@@ -615,7 +615,7 @@ def _update_config_file(
 
         if write_to_config_file:
             with open(config_file, "wt", encoding="utf-8", newline=config_newlines) as f:
-                f.write(new_config.getvalue())
+                f.write(new_config.getvalue().strip() + "\n")
 
     except UnicodeEncodeError:
         warnings.warn(

tests/test_cli.py

@@ -312,7 +312,6 @@ def test_config_file_is_updated(tmpdir):
 current_version = 0.0.14
 
 [bumpversion:file:file3]
-
 """ == tmpdir.join(".bumpversion.cfg").read()
 
 
@@ -1990,7 +1989,12 @@ def test_retain_newline(tmpdir, configfile, newline):
     main(["major"])
 
     assert newline in tmpdir.join("file.py").read_binary()
-    assert newline in tmpdir.join(configfile).read_binary()
+    new_config = tmpdir.join(configfile).read_binary()
+    assert newline in new_config
+
+    # Ensure there is only a single newline (not two) at the end of the file
+    # and that it is of the right type
+    assert new_config.endswith(b"[bumpversion:file:file.py]" + newline)
 
 
 class TestSplitArgsInOptionalAndPositional: