Add basic oneof tests

README.md

@@ -222,6 +222,10 @@ $ pipenv run tests
 - [x] Refs to nested types
 - [x] Imports in proto files
 - [x] Well-known Google types
+- [ ] OneOf support
+  - [x] Basic support on the wire
+  - [ ] Check which was set from the group
+  - [ ] Setting one unsets the others
 - [ ] JSON that isn't completely naive.
   - [x] 64-bit ints as strings
   - [x] Maps

betterproto/tests/oneof-name.json

@@ -0,0 +1,3 @@
+{
+  "name": "foo"
+}

betterproto/tests/oneof.json

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

betterproto/tests/oneof.proto

@@ -0,0 +1,8 @@
+syntax = "proto3";
+
+message Test {
+  oneof foo {
+    int32 count = 1;
+    string name = 2;
+  }
+}