@Override
        public ApplicationFile writeFile(Reader input) {
            if (content != null) throw new UnsupportedOperationException("Not implemented for mock file content");
            uncheck(() -> IOUtils.writeFile(file, IOUtils.readAll(input), false));
            return this;
        }
The content of this file, or null to read it from the file system.
config-model/src/main/java/com/yahoo/config/model/test/MockApplicationPackage.java