### Question:
DataSourceRule { public Collection<String> getDataSourceNames() { return dataSourceMap.keySet(); } DataSourceRule(final Map<String, DataSource> dataSourceMap);  DataSourceRule(final Map<String, DataSource> dataSourceMap, final String defaultDataSourceName); DataSource getDataSource(final String name); Optional<DataSource> getDefaultDataSource(); Collection<String> getDataSourceNames(); Collection<DataSource> getDataSources();  }### Answer:
@Test public void assertGetDataSourceNames() { assertThat(dataSourceRule.getDataSourceNames(), is((Collection<String>) Sets.newHashSet("ds0", "ds1", "ds2"))); }