### Question:
SessionIdFormat { @Nonnull public String createBackupKey( @Nonnull final String origKey ) { if ( origKey == null ) { throw new IllegalArgumentException( "The origKey must not be null." ); } return BACKUP_PREFIX + _storageKeyFormat.format(origKey); } SessionIdFormat();  SessionIdFormat(final StorageKeyFormat storageKeyFormat); @Nonnull String createSessionId(@Nonnull final String sessionId, @Nullable final String memcachedId); @Nonnull String createNewSessionId( @Nonnull final String sessionId, @Nonnull final String newMemcachedId); @Nonnull String changeJvmRoute( @Nonnull final String sessionId, @Nonnull final String newJvmRoute ); boolean isValid( @Nullable final String sessionId ); @CheckForNull String extractMemcachedId( @Nonnull final String sessionId ); @CheckForNull String extractJvmRoute( @Nonnull final String sessionId ); @Nonnull String stripJvmRoute( @Nonnull final String sessionId ); @Nonnull String createLockName( @Nonnull final String sessionId ); @Nonnull String createValidityInfoKeyName( @Nonnull final String origKey ); @Nonnull String createBackupKey( @Nonnull final String origKey ); boolean isBackupKey( @Nonnull final String key );  }### Answer:
@Test public void testCreateBackupKey() { final SessionIdFormat cut = new SessionIdFormat(StorageKeyFormat.ofHost("localhost")); assertEquals(cut.createBackupKey("foo"), "bak:localhost_foo"); }