Properly serialize zero-value messages in a oneof group (#176)

Also improve test utils to make it easier to have multiple json examples.

Co-authored-by: Christopher Chambers <chris@peanutcode.com>

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")

tests/inputs/oneof_empty/oneof_empty.json

@@ -0,0 +1,3 @@
+{
+  "nothing": {}
+}

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;
+  }
+}

tests/inputs/oneof_empty/oneof_empty_maybe1.json

@@ -0,0 +1,3 @@
+{
+  "maybe1": {}
+}

tests/inputs/oneof_empty/oneof_empty_maybe2.json

@@ -0,0 +1,5 @@
+{
+  "maybe2": {
+    "sometimes": "now"
+  }
+}

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))