PropertyStatistics { public Set<String> getKeys() { return issuesByProperty.keySet(); } PropertyStatistics(final Report report,
            final String property, final Function<String, String> propertyFormatter); int getTotal(); String getProperty(); String getDisplayName(final String key); String getToolTip(final String key); Set<String> getKeys(); int getMax(); long getCount(final String key); long getErrorsCount(final String key); long getHighCount(final String key); long getNormalCount(final String key); long getLowCount(final String key);  }
@Test void shouldReturnEmptyKeys() { PropertyStatistics statistics = new PropertyStatistics(new Report(), "category", Function.identity()); Set<String> actualProperty = statistics.getKeys(); assertThat(actualProperty).isEmpty(); }