### Question:
GrainProperties { public Map<Map.Entry<String, String>, Collection<String>> getHostsPerGrainMap() { ArrayListMultimap<Map.Entry<String, String>, String> multimap = ArrayListMultimap.create(); getProperties().forEach((host, grainMap) -> grainMap.entrySet().forEach(grain -> multimap.put(grain, host))); return multimap.asMap(); }  Map<String, String> computeIfAbsent(String key, Function<? super String, ? extends Map<String, String>> mappingFunction); Map<String, String> put(String key, Map<String, String> value); Map<String, Map<String, String>> getProperties(); Map<Map.Entry<String, String>, Collection<String>> getHostsPerGrainMap();  }### Answer:
@Test public void whenPropertyIsEmptyThenHostsPerGrainMapEmpty() { Map<Entry<String, String>, Collection<String>> hostsPerGrainMap = underTest.getHostsPerGrainMap(); assertTrue(hostsPerGrainMap.isEmpty()); }