### Question:
UserDbUtils { public static String createFileName(String username) { String usernameLower = username.toLowerCase(); String usernameHash = hashString(usernameLower); String filename = String.format("%s.db", usernameHash); return filename; } private  UserDbUtils(); static DbContext createDbContext(final Path dbPath); static String createFileName(String username);  }### Answer:
@Test public void testCreateFileName() { String sha256 = "96d9632f363564cc3032521409cf22a852f2032eec099ed5967c0d000cec607a"; String username = "John"; String filename = UserDbUtils.createFileName(username); String expected = String.format("%s.db", sha256); assertEquals(expected, filename); filename = UserDbUtils.createFileName(username.toLowerCase()); assertEquals(expected, filename); filename = UserDbUtils.createFileName(username.toUpperCase()); assertEquals(expected, filename); }