chore(test): Tests protobuf.d.ts

Applies runtime assertions to ensure that returned values adhere to their qualified type.

protobufjs/test.proto

@@ -0,0 +1,30 @@
+// Everything below is located in the js-namespace
+package js;
+
+// Represents a JavaScript value.
+// Contains exactly one or zero fields.
+message Value {
+    oneof type {
+        sint32 integer = 1;
+        double double = 2;
+        string string = 3;
+        bool boolean = 4;
+        bool null = 5;
+        Array array = 6;
+        Object object = 7;
+        // if none is set: undefined
+    }
+}
+
+// Represents a JavaScript array.
+// Contains zero to N values.
+message Array {
+    repeated Value values = 1;
+}
+
+// Represents a JavaScript object.
+// Contains zero to N keys with associated values.
+message Object {
+    repeated Value keys = 1;
+    repeated Value values = 2;
+}