public void intersectCategories() {
Collection<Category> cat1 = new ArrayList<Category>();
Collection<Category> cat2 = new ArrayList<Category>();
assertEquals(Collections.emptyList(), Utils.intersectCategories(cat1, cat2));
cat1.add(new Category("db", "SqlServer"));
assertEquals(1, Utils.intersectCategories(cat1, null).size());
cat2.add(new Category("db", "SqlServer"));
assertEquals(1, Utils.intersectCategories(cat1, cat2).size());
cat2.add(new Category("Main"));
assertEquals(2, Utils.intersectCategories(cat1, cat2).size());
cat2.add(new Category("db", "Oracle"));
assertEquals(2, Utils.intersectCategories(cat1, cat2).size());
cat1.add(new Category("Repository"));
assertEquals(0, Utils.intersectCategories(cat1, cat2).size());
}