@Override
    public Path writeFile(Path path, Reader fileContentsReader) {
        StringBuilder builder = new StringBuilder();
        char[] buffer = new char[8 * 1024];
        int numCharsRead;
        try {
            while ((numCharsRead = fileContentsReader.read(buffer, 0, buffer.length)) != -1) {
                builder.append(buffer, 0, numCharsRead);
            }
        } catch (IOException e) {
            throw new SmithyBuildException(e);
        }

        return storeFile(path, builder.toString().getBytes(Charset.forName("UTF-8")));
    }
Creates a mock manifest that stores files in memory and uses a
base directory of "/".
smithy-build/src/main/java/software/amazon/smithy/build/MockManifest.java