### Question:
FieldValuePrefixAdder { public String prefixWithSeparator(String fieldValuePrefix) { Preconditions.checkNotNull(fieldValuePrefix); return fieldValuePrefix + FIELD_VALUE_PREFIX_SEPARATOR; }  String addFieldPrefix(String prefix, String fieldValue); String prefixWithSeparator(String fieldValuePrefix); String extractFieldValue(String valueWithPrefix);  }### Answer:
@Test(expected = NullPointerException.class) public void prefixWithSeparator_NULL() { fieldValuePrefixAdder.prefixWithSeparator(null); }
@Test public void prefixWithSeparator() { assertEquals("ALA_MA_KOTA"+FIELD_VALUE_PREFIX_SEPARATOR, fieldValuePrefixAdder.prefixWithSeparator("ALA_MA_KOTA")); }