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