### Question:
ClientCredentials { @Override public String toString() { return String.format("%s:%s", clientId, clientSecret); } ClientCredentials(@Nonnull String clientId, @Nonnull String clientSecret); String getSecret(); String getId(); @Override boolean equals(Object o); @Override int hashCode(); @Override String toString();  }### Answer:
@Test public void stringify() { assertThat(cut.toString(), is("clientId:clientSecret")); }