### Question:
InMemoryUserIdentityManager implements UsersIdentityManager, Configurable { @Override public void configure(final Conf configuration) { LOG.debug("Configuring user identities from props: '{}'", SecurityConfig.REST_AUTHENTICATION_USERS_CONFIG); SecurityConfig securityConfig = new SecurityConfig(configuration); final String[] users = securityConfig.getAuthenticationUsers().split(","); Arrays.stream(users) .map(String::trim) .forEach(user -> { String[] upwd = user.split(":", 2); if (upwd.length < 2) { throw new SecurityConfException( "Invalid config for '" + SecurityConfig.REST_AUTHENTICATION_USERS_CONFIG + "', Expecting <user>:<password>." ); } addUsers(new UserDetails(upwd[0], PasswordCredentials.get(upwd[1]))); LOG.debug("Add user credentials for '{}'", upwd[0]); }); if (users.length == 0) { LOG.debug("No user configured"); } } InMemoryUserIdentityManager(); private  InMemoryUserIdentityManager(final Map<String, UserDetails> users); void addUsers(final UserDetails user); UserDetails deleteUsersByName(final String name); Set<String> getUsers(); @Override UserDetails findUserByName(final String name); @Override void configure(final Conf configuration);  }### Answer:
@Test public void shouldThrowSecurityExceptionGivenInvalidConfig() { final InMemoryUserIdentityManager manager = new InMemoryUserIdentityManager(); Assertions.assertThrows(SecurityConfException.class, () -> manager.configure(Conf.of(SecurityConfig.REST_AUTHENTICATION_USERS_CONFIG, "alice")) ); }