diff --git a/pre_commit_hooks/pretty_format_json.py b/pre_commit_hooks/pretty_format_json.py
index d9956fe..f3afe98 100644
--- a/pre_commit_hooks/pretty_format_json.py
+++ b/pre_commit_hooks/pretty_format_json.py
@@ -9,9 +9,11 @@ from difflib import unified_diff
 from typing import Mapping
 from typing import Sequence
 
-def _insert_linebreaks(json_str) -> str:
-    # (?P<spaces>\s*) seems to capture the \n. Hence, there is no need for it in the substitution string
-    return re.sub(r'\n(?P<spaces>\s*)(?P<json_key>.*): {}(?P<delim>,??)', '\n\g<spaces>\g<json_key>: {\n\g<spaces>}\g<delim>', json_str)
+def _insert_linebreaks(json_str: str) -> str:
+    return re.sub(
+        r'\n(?P<spaces>\s*)(?P<json_key>.*): {}(?P<delim>,??)', 
+        '\n\g<spaces>\g<json_key>: {\n\g<spaces>}\g<delim>', 
+        json_str)
 
 def _get_pretty_format(
         contents: str,
@@ -109,7 +111,8 @@ def main(argv: Sequence[str] | None = None) -> int:
         action='store_true',
         dest='empty_object_with_newline',
         default=False,
-        help='Format empty JSON objects to have a linebreak, also activates --no-sort-keys',
+        help='Format empty JSON objects to have a linebreak, ' \
+            + 'also activates --no-sort-keys',
     )
     parser.add_argument('filenames', nargs='*', help='Filenames to fix')
     args = parser.parse_args(argv)
diff --git a/tests/pretty_format_json_test.py b/tests/pretty_format_json_test.py
index 31f3955..4413d17 100644
--- a/tests/pretty_format_json_test.py
+++ b/tests/pretty_format_json_test.py
@@ -146,24 +146,29 @@ def test_empty_object_with_newline(tmpdir):
     ret = main(["--empty-object-with-newline", str(sameline)])
     assert ret == 1
 
+    # a template to be compared against.
     multiline = get_resource_path("empty_object_json_multiline.json")
-    to_be_formatted_sameline = tmpdir.join(
-        "not_pretty_formatted_empty_object_json_sameline.json"
-    )
-    shutil.copyfile(str(sameline), str(to_be_formatted_sameline))
 
     # file has empty object with newline => expect fail with default settings
     ret = main([str(multiline)])
     assert ret == 1
 
-    # now launch the autofix with empty object with newline support on that file
+    # launch the autofix with empty object with newline support on that file
+    to_be_formatted_sameline = tmpdir.join(
+        "not_pretty_formatted_empty_object_json_sameline.json"
+    )
+    shutil.copyfile(str(sameline), str(to_be_formatted_sameline))
     ret = main(
-        ["--autofix", "--empty-object-with-newline", str(to_be_formatted_sameline)]
+        ["--autofix",
+        "--empty-object-with-newline",
+        str(to_be_formatted_sameline)]
     )
     # it should have formatted it and don't raise an error code
+    # to not stop the the commit
     assert ret == 0
 
-    # file was formatted (shouldn't trigger linter with --empty-object-with-newline switch)
+    # file was formatted (shouldn't trigger linter with 
+    # --empty-object-with-newline switch)
     ret = main(["--empty-object-with-newline", str(to_be_formatted_sameline)])
     assert ret == 0
     assert filecmp.cmp(to_be_formatted_sameline, multiline)