diff --git a/pyproject.toml b/pyproject.toml
index a93a96e..114209f 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -49,9 +49,9 @@ generate    = { script = "tests.generate:main", help = "Generate test cases (do
 test        = { cmd = "pytest --cov src", help = "Run tests" }
 types       = { cmd = "mypy src --ignore-missing-imports", help = "Check types with mypy" }
 format      = { cmd = "black . --exclude tests/output_",   help = "Apply black formatting to source code" }
-clean       = { cmd = "rm -rf .coverage .mypy_cache .pytest_cache dist betterproto.egg-info **/__pycache__ tests/output_*", help = "Clean out generated files from the workspace" }
 docs        = { cmd = "sphinx-build docs docs/build", help = "Build the sphinx docs"}
 bench       = { shell = "asv run master^! && asv run HEAD^! && asv compare master HEAD", help = "Benchmark current commit vs. master branch"}
+clean       = { cmd = "rm -rf .asv .coverage .mypy_cache .pytest_cache dist betterproto.egg-info **/__pycache__ tests/output_*", help  = "Clean out generated files from the workspace" }
 
 # CI tasks
 full-test   = { shell = "poe generate && tox", help = "Run tests with multiple pythons" }
diff --git a/src/betterproto/__init__.py b/src/betterproto/__init__.py
index f73c3f4..48a7358 100644
--- a/src/betterproto/__init__.py
+++ b/src/betterproto/__init__.py
@@ -699,7 +699,7 @@ class Message(ABC):
                     meta.number,
                     meta.proto_type,
                     value,
-                    serialize_empty=serialize_empty,
+                    serialize_empty=serialize_empty or selected_in_group,
                     wraps=meta.wraps or "",
                 )
 
diff --git a/tests/inputs/oneof/oneof-name.json b/tests/inputs/oneof/oneof_name.json
similarity index 100%
rename from tests/inputs/oneof/oneof-name.json
rename to tests/inputs/oneof/oneof_name.json
diff --git a/tests/inputs/oneof/test_oneof.py b/tests/inputs/oneof/test_oneof.py
index c361b53..8a1d3ea 100644
--- a/tests/inputs/oneof/test_oneof.py
+++ b/tests/inputs/oneof/test_oneof.py
@@ -5,11 +5,11 @@ from tests.util import get_test_case_json_data
 
 def test_which_count():
     message = Test()
-    message.from_json(get_test_case_json_data("oneof"))
+    message.from_json(get_test_case_json_data("oneof")[0])
     assert betterproto.which_one_of(message, "foo") == ("count", 100)
 
 
 def test_which_name():
     message = Test()
-    message.from_json(get_test_case_json_data("oneof", "oneof-name.json"))
+    message.from_json(get_test_case_json_data("oneof", "oneof_name.json")[0])
     assert betterproto.which_one_of(message, "foo") == ("name", "foobar")
diff --git a/tests/inputs/oneof_empty/oneof_empty.json b/tests/inputs/oneof_empty/oneof_empty.json
new file mode 100644
index 0000000..9d21c89
--- /dev/null
+++ b/tests/inputs/oneof_empty/oneof_empty.json
@@ -0,0 +1,3 @@
+{
+  "nothing": {}
+}
diff --git a/tests/inputs/oneof_empty/oneof_empty.proto b/tests/inputs/oneof_empty/oneof_empty.proto
new file mode 100644
index 0000000..45ca371
--- /dev/null
+++ b/tests/inputs/oneof_empty/oneof_empty.proto
@@ -0,0 +1,15 @@
+syntax = "proto3";
+
+message Nothing {}
+
+message MaybeNothing {
+  string sometimes = 42;
+}
+
+message Test {
+  oneof empty {
+    Nothing nothing = 1;
+    MaybeNothing maybe1 = 2;
+    MaybeNothing maybe2 = 3;
+  }
+}
diff --git a/tests/inputs/oneof_empty/oneof_empty_maybe1.json b/tests/inputs/oneof_empty/oneof_empty_maybe1.json
new file mode 100644
index 0000000..f7a2d27
--- /dev/null
+++ b/tests/inputs/oneof_empty/oneof_empty_maybe1.json
@@ -0,0 +1,3 @@
+{
+  "maybe1": {}
+}
diff --git a/tests/inputs/oneof_empty/oneof_empty_maybe2.json b/tests/inputs/oneof_empty/oneof_empty_maybe2.json
new file mode 100644
index 0000000..bc2b385
--- /dev/null
+++ b/tests/inputs/oneof_empty/oneof_empty_maybe2.json
@@ -0,0 +1,5 @@
+{
+  "maybe2": {
+    "sometimes": "now"
+  }
+}
diff --git a/tests/inputs/oneof_empty/test_oneof_empty.py b/tests/inputs/oneof_empty/test_oneof_empty.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/inputs/oneof_enum/test_oneof_enum.py b/tests/inputs/oneof_enum/test_oneof_enum.py
index e3eca13..73b37c6 100644
--- a/tests/inputs/oneof_enum/test_oneof_enum.py
+++ b/tests/inputs/oneof_enum/test_oneof_enum.py
@@ -14,7 +14,9 @@ def test_which_one_of_returns_enum_with_default_value():
     returns first field when it is enum and set with default value
     """
     message = Test()
-    message.from_json(get_test_case_json_data("oneof_enum", "oneof_enum-enum-0.json"))
+    message.from_json(
+        get_test_case_json_data("oneof_enum", "oneof_enum-enum-0.json")[0]
+    )
 
     assert message.move == Move(
         x=0, y=0
@@ -28,7 +30,9 @@ def test_which_one_of_returns_enum_with_non_default_value():
     returns first field when it is enum and set with non default value
     """
     message = Test()
-    message.from_json(get_test_case_json_data("oneof_enum", "oneof_enum-enum-1.json"))
+    message.from_json(
+        get_test_case_json_data("oneof_enum", "oneof_enum-enum-1.json")[0]
+    )
     assert message.move == Move(
         x=0, y=0
     )  # Proto3 will default this as there is no null
@@ -38,7 +42,7 @@ def test_which_one_of_returns_enum_with_non_default_value():
 
 def test_which_one_of_returns_second_field_when_set():
     message = Test()
-    message.from_json(get_test_case_json_data("oneof_enum"))
+    message.from_json(get_test_case_json_data("oneof_enum")[0])
     assert message.move == Move(x=2, y=3)
     assert message.signal == Signal.PASS
     assert betterproto.which_one_of(message, "action") == ("move", Move(x=2, y=3))
diff --git a/tests/test_features.py b/tests/test_features.py
index 9bf30e6..3f44f17 100644
--- a/tests/test_features.py
+++ b/tests/test_features.py
@@ -286,17 +286,23 @@ def test_to_dict_default_values():
 
 
 def test_oneof_default_value_set_causes_writes_wire():
+    @dataclass
+    class Empty(betterproto.Message):
+        pass
+
     @dataclass
     class Foo(betterproto.Message):
         bar: int = betterproto.int32_field(1, group="group1")
         baz: str = betterproto.string_field(2, group="group1")
+        qux: Empty = betterproto.message_field(3, group="group1")
 
     def _round_trip_serialization(foo: Foo) -> Foo:
         return Foo().parse(bytes(foo))
 
     foo1 = Foo(bar=0)
     foo2 = Foo(baz="")
-    foo3 = Foo()
+    foo3 = Foo(qux=Empty())
+    foo4 = Foo()
 
     assert bytes(foo1) == b"\x08\x00"
     assert (
@@ -312,10 +318,17 @@ def test_oneof_default_value_set_causes_writes_wire():
         == ("baz", "")
     )
 
-    assert bytes(foo3) == b""
+    assert bytes(foo3) == b"\x1a\x00"
     assert (
         betterproto.which_one_of(foo3, "group1")
         == betterproto.which_one_of(_round_trip_serialization(foo3), "group1")
+        == ("qux", Empty())
+    )
+
+    assert bytes(foo4) == b""
+    assert (
+        betterproto.which_one_of(foo4, "group1")
+        == betterproto.which_one_of(_round_trip_serialization(foo4), "group1")
         == ("", None)
     )
 
diff --git a/tests/test_inputs.py b/tests/test_inputs.py
index f09ee79..e743f64 100644
--- a/tests/test_inputs.py
+++ b/tests/test_inputs.py
@@ -126,42 +126,44 @@ def test_message_json(repeat, test_data: TestData) -> None:
     plugin_module, _, json_data = test_data
 
     for _ in range(repeat):
-        message: betterproto.Message = plugin_module.Test()
+        for json_sample in json_data:
+            message: betterproto.Message = plugin_module.Test()
 
-        message.from_json(json_data)
-        message_json = message.to_json(0)
+            message.from_json(json_sample)
+            message_json = message.to_json(0)
 
-        assert json.loads(message_json) == json.loads(json_data)
+            assert json.loads(message_json) == json.loads(json_sample)
 
 
 @pytest.mark.parametrize("test_data", test_cases.services, indirect=True)
 def test_service_can_be_instantiated(test_data: TestData) -> None:
-    plugin_module, _, json_data = test_data
-    plugin_module.TestStub(MockChannel())
+    test_data.plugin_module.TestStub(MockChannel())
 
 
 @pytest.mark.parametrize("test_data", test_cases.messages_with_json, indirect=True)
 def test_binary_compatibility(repeat, test_data: TestData) -> None:
     plugin_module, reference_module, json_data = test_data
 
-    reference_instance = Parse(json_data, reference_module().Test())
-    reference_binary_output = reference_instance.SerializeToString()
+    for json_sample in json_data:
+        reference_instance = Parse(json_sample, reference_module().Test())
+        reference_binary_output = reference_instance.SerializeToString()
 
-    for _ in range(repeat):
-        plugin_instance_from_json: betterproto.Message = plugin_module.Test().from_json(
-            json_data
-        )
-        plugin_instance_from_binary = plugin_module.Test.FromString(
-            reference_binary_output
-        )
+        for _ in range(repeat):
+            plugin_instance_from_json: betterproto.Message = (
+                plugin_module.Test().from_json(json_sample)
+            )
+            plugin_instance_from_binary = plugin_module.Test.FromString(
+                reference_binary_output
+            )
 
-        # # Generally this can't be relied on, but here we are aiming to match the
-        # # existing Python implementation and aren't doing anything tricky.
-        # # https://developers.google.com/protocol-buffers/docs/encoding#implications
-        assert bytes(plugin_instance_from_json) == reference_binary_output
-        assert bytes(plugin_instance_from_binary) == reference_binary_output
+            # # Generally this can't be relied on, but here we are aiming to match the
+            # # existing Python implementation and aren't doing anything tricky.
+            # # https://developers.google.com/protocol-buffers/docs/encoding#implications
+            assert bytes(plugin_instance_from_json) == reference_binary_output
+            assert bytes(plugin_instance_from_binary) == reference_binary_output
 
-        assert plugin_instance_from_json == plugin_instance_from_binary
-        assert (
-            plugin_instance_from_json.to_dict() == plugin_instance_from_binary.to_dict()
-        )
+            assert plugin_instance_from_json == plugin_instance_from_binary
+            assert (
+                plugin_instance_from_json.to_dict()
+                == plugin_instance_from_binary.to_dict()
+            )
diff --git a/tests/util.py b/tests/util.py
index 6c63141..5dcf155 100644
--- a/tests/util.py
+++ b/tests/util.py
@@ -5,7 +5,7 @@ import pathlib
 import sys
 from pathlib import Path
 from types import ModuleType
-from typing import Callable, Generator, Optional, Union
+from typing import Callable, Generator, List, Optional, Union
 
 os.environ["PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION"] = "python"
 
@@ -47,15 +47,27 @@ async def protoc(
     return stdout, stderr, proc.returncode
 
 
-def get_test_case_json_data(test_case_name: str, json_file_name: Optional[str] = None):
-    test_data_file_name = json_file_name or f"{test_case_name}.json"
-    test_data_file_path = inputs_path.joinpath(test_case_name, test_data_file_name)
+def get_test_case_json_data(test_case_name: str, *json_file_names: str) -> List[str]:
+    """
+    :return:
+        A list of all files found in "inputs_path/test_case_name" with names matching
+        f"{test_case_name}.json" or f"{test_case_name}_*.json", OR given by json_file_names
+    """
+    test_case_dir = inputs_path.joinpath(test_case_name)
+    possible_file_paths = [
+        *(test_case_dir.joinpath(json_file_name) for json_file_name in json_file_names),
+        test_case_dir.joinpath(f"{test_case_name}.json"),
+        *test_case_dir.glob(f"{test_case_name}_*.json"),
+    ]
 
-    if not test_data_file_path.exists():
-        return None
+    result = []
+    for test_data_file_path in possible_file_paths:
+        if not test_data_file_path.exists():
+            continue
+        with test_data_file_path.open("r") as fh:
+            result.append(fh.read())
 
-    with test_data_file_path.open("r") as fh:
-        return fh.read()
+    return result
 
 
 def find_module(