@Override
        public ApplicationFile appendFile(String value) {
            try {
                if (content != null) throw new UnsupportedOperationException("Not implemented for mock file content");
                IOUtils.writeFile(file, value, true);
                return this;
            }
            catch (IOException e) {
                throw new UncheckedIOException(e);
            }
        }
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