diff --git a/internal/protobuf/protobuf_test.go b/internal/protobuf/protobuf_test.go
new file mode 100644
index 0000000..d75126d
--- /dev/null
+++ b/internal/protobuf/protobuf_test.go
@@ -0,0 +1,68 @@
+// Copyright 2019 CUE Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package protobuf
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"path/filepath"
+	"testing"
+
+	"cuelang.org/go/cue/format"
+	"github.com/kr/pretty"
+)
+
+var update *bool = flag.Bool("update", false, "update the test output")
+
+func TestParseDefinitions(t *testing.T) {
+	testCases := []string{
+		"networking/v1alpha3/gateway.proto",
+		"mixer/v1/attributes.proto",
+		"mixer/v1/config/client/client_config.proto",
+	}
+	for _, file := range testCases {
+		t.Run(file, func(t *testing.T) {
+			filename := filepath.Join("testdata", filepath.FromSlash(file))
+			c := &Config{
+				Paths: []string{"testdata"},
+			}
+
+			out := &bytes.Buffer{}
+
+			if f, err := Parse(filename, nil, c); err != nil {
+				fmt.Fprintln(out, err)
+			} else {
+				format.Node(out, f)
+			}
+
+			wantFile := filepath.Join("testdata", filepath.Base(file)+".out.cue")
+			if *update {
+				ioutil.WriteFile(wantFile, out.Bytes(), 0644)
+				return
+			}
+
+			b, err := ioutil.ReadFile(wantFile)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			if desc := pretty.Diff(out.String(), string(b)); len(desc) > 0 {
+				t.Errorf("files differ:\n%v", desc)
+			}
+		})
+	}
+}