Add return type to tests without arguments (#87613)

* Add return type to tests without arguments

* Black

* Cancel fixture amends

tests/util/test_json.py

@@ -44,7 +44,7 @@ def _path_for(leaf_name):
     return os.path.join(TMP_DIR, f"{leaf_name}.json")
 
 
-def test_save_and_load():
+def test_save_and_load() -> None:
     """Test saving and loading back."""
     fname = _path_for("test1")
     save_json(fname, TEST_JSON_A)
@@ -52,7 +52,7 @@ def test_save_and_load():
     assert data == TEST_JSON_A
 
 
-def test_save_and_load_int_keys():
+def test_save_and_load_int_keys() -> None:
     """Test saving and loading back stringifies the keys."""
     fname = _path_for("test1")
     save_json(fname, {1: "a", 2: "b"})
@@ -60,7 +60,7 @@ def test_save_and_load_int_keys():
     assert data == {"1": "a", "2": "b"}
 
 
-def test_save_and_load_private():
+def test_save_and_load_private() -> None:
     """Test we can load private files and that they are protected."""
     fname = _path_for("test2")
     save_json(fname, TEST_JSON_A, private=True)
@@ -80,7 +80,7 @@ def test_overwrite_and_reload(atomic_writes):
     assert data == TEST_JSON_B
 
 
-def test_save_bad_data():
+def test_save_bad_data() -> None:
     """Test error from trying to save unserializable data."""
 
     class CannotSerializeMe:
@@ -94,7 +94,7 @@ def test_save_bad_data():
     )
 
 
-def test_load_bad_data():
+def test_load_bad_data() -> None:
     """Test error from trying to load unserialisable data."""
     fname = _path_for("test5")
     with open(fname, "w") as fh:
@@ -103,7 +103,7 @@ def test_load_bad_data():
         load_json(fname)
 
 
-def test_custom_encoder():
+def test_custom_encoder() -> None:
     """Test serializing with a custom encoder."""
 
     class MockJSONEncoder(JSONEncoder):
@@ -119,7 +119,7 @@ def test_custom_encoder():
     assert data == "9"
 
 
-def test_default_encoder_is_passed():
+def test_default_encoder_is_passed() -> None:
     """Test we use orjson if they pass in the default encoder."""
     fname = _path_for("test6")
     with patch(
@@ -134,7 +134,7 @@ def test_default_encoder_is_passed():
     assert data == {"any": [1]}
 
 
-def test_find_unserializable_data():
+def test_find_unserializable_data() -> None:
     """Find unserializeable data."""
     assert find_paths_unserializable_data(1) == {}
     assert find_paths_unserializable_data([1, 2]) == {}