### Question:
SolutionIndex { public Iterator<Solution<T>> composeSolutions(final String variable, final T value, final Solution<T> ps, final long now) { Iterator<Solution<T>> iter = getSolutions(variable, value, now); return null == iter ? null : new FilteredIterator<Solution<T>, Solution<T>>(iter) { @Override protected Solution<T> test(final Solution<T> element) { return ps.composableWith(element, queryVariables) ? new Solution<>(totalPatterns, ps, element) : null; } }; } SolutionIndex(final Query.QueryVariables queryVariables,
                         final int totalPatterns); synchronized boolean add(final Solution<T> s, final long now); Iterator<Solution<T>> getSolutions(final String variable, final T value, final long now); Iterator<Solution<T>> getComposableSolutions(final String variable,
                                                        final T value,
                                                        final Solution<T> ps,
                                                        final long now); Iterator<Solution<T>> composeSolutions(final String variable,
                                                  final T value,
                                                  final Solution<T> ps,
                                                  final long now); void joinSolutions(final Solution<T> matchedSolution,
                              final Bindings<T> bindings,
                              final Stack<Solution<T>> solutions,
                              final long now); synchronized int removeExpired(final long now);  }### Answer:
@Test public void testComposeSolutions() throws Exception { HashMap<String, String> map1, map2; Bindings<String> b1, b2; Solution<String> ps1, ps2; map1 = new HashMap<>(); map1.put("x", "red"); map1.put("z", "blue"); b1 = new Bindings<>(map1, vars); ps1 = new Solution<>(3, 0, b1, exp); map2 = new HashMap<>(); map2.put("y", "green"); b2 = new Bindings<>(map2, vars); ps2 = new Solution<>(ps1, 2, b2); index.add(ps2, now); assertEquals(0, count(index.composeSolutions("x", "red", ps1, now))); map2 = new HashMap<>(); map2.put("x", "red"); map2.put("y", "green"); b2 = new Bindings<>(map2, vars); ps2 = new Solution<>(3, 2, b2, exp); index.add(ps2, now); assertEquals(1, count(index.composeSolutions("x", "red", ps1, now))); map2 = new HashMap<>(); map2.put("x", "red"); map2.put("y", "hazel"); b2 = new Bindings<>(map2, vars); ps2 = new Solution<>(3, 2, b2, exp); index.add(ps2, now); assertEquals(2, count(index.composeSolutions("x", "red", ps1, now))); }