### Question:
XmppAccountConfiguration extends JObject implements AccountConfiguration { @Nullable public static String getAfterAt(@Nonnull String s) { final int index = s.indexOf(AT); if (index < 0) { return null; } else { return s.substring(index + 1); } } XmppAccountConfiguration();  XmppAccountConfiguration(@Nonnull String server, @Nonnull String login, @Nonnull String password); @Nonnull String getAccountUserId(); @Nullable String getDomain(); @Nonnull String getServer(); @Nonnull String getLogin(); @Nonnull String getLoginForConnection(); @Nonnull String getPassword(); @Nonnull XmppSecurityMode getSecurityMode(); void setSecurityMode(@Nonnull XmppSecurityMode securityMode); boolean isUseLoginWithDomain(); void setUseLoginWithDomain(boolean useLoginWithDomain); @Nonnull String getResource(); @Nonnull Integer getPort(); @Nonnull AndroidConnectionConfiguration toXmppConfiguration(); @Override boolean isSameAccount(AccountConfiguration c); @Override boolean isSameCredentials(AccountConfiguration c); @Override boolean isSame(AccountConfiguration c); @Override void applySystemData(AccountConfiguration oldConfiguration); @Nonnull static XmppAccountConfiguration fromJson(@Nonnull String json); @Nonnull @Override XmppAccountConfiguration clone(); void setPassword(@Nonnull String password); @Nullable static String getAfterAt(@Nonnull String s); @Nonnull static String getBeforeAt(@Nonnull String s);  }### Answer:
@Test public void testShouldReturnNullIfNoAtExists() throws Exception { assertNull(getAfterAt("test")); assertNull(getAfterAt("")); }
@Test public void testShouldReturnEmptyStringIfAtIsLastSymbol() throws Exception { assertEquals("", getAfterAt("test@")); assertEquals("", getAfterAt("@")); assertEquals("", getAfterAt("wetwegdfgsdfgsfdgsdfg@")); }
@Test public void testShouldReturnEverythingAfterFirstAt() throws Exception { assertEquals("test2", getAfterAt("test@test2")); assertEquals("e", getAfterAt("@e")); assertEquals("qwer@trew", getAfterAt("test@qwer@trew")); }