### Question:
NamingConventions { public static String convertToLowerUnderscore(String identifierName) { return splitToLowercaseTerms(identifierName).stream().collect(Collectors.joining("_")); }  static ImmutableList<String> splitToLowercaseTerms(String identifierName); static String convertToLowerUnderscore(String identifierName);  }### Answer:
@Test public void convertToLowerUnderscore_givesSingleUnderscore_fromSingleUnderscore() { String identifierName = "_"; String lowerUnderscore = NamingConventions.convertToLowerUnderscore(identifierName); assertThat(lowerUnderscore).isEqualTo("_"); }
@Test public void convertToLowerUnderscore_separatesTerms_fromCamelCase() { String identifierName = "camelCase"; String lowerUnderscore = NamingConventions.convertToLowerUnderscore(identifierName); assertThat(lowerUnderscore).isEqualTo("camel_case"); }