### Question:
SubSetGraph { public boolean isEmpty() { return subGraphs.isEmpty(); }  SubSetGraph add(ColumnCombinationBitset columnCombination); SubSetGraph addAll(Collection<ColumnCombinationBitset> columnCombinations); ArrayList<ColumnCombinationBitset> getExistingSubsets(
    ColumnCombinationBitset columnCombinationToQuery); boolean containsSubset(ColumnCombinationBitset superset); Set<ColumnCombinationBitset> getMinimalSubsets(); boolean isEmpty(); @Override boolean equals(Object o); @Override int hashCode();  }### Answer:
@Test public void testIsEmpty() { SubSetGraph emptyGraph = new SubSetGraph(); SubSetGraph nonEmptyGraph = new SubSetGraph(); nonEmptyGraph.add(new ColumnCombinationBitset(10)); assertTrue(emptyGraph.isEmpty()); assertFalse(nonEmptyGraph.isEmpty()); }