svoid test_startsWithOneOf_treeSet() {
  assertTrue("potato 1", startsWithOneOf_treeSet("potato", littreeset("pot")));
  assertTrue("potato 2", startsWithOneOf_treeSet("potato", littreeset("pot", "potash")));
  assertTrue("potato 3", startsWithOneOf_treeSet("potato", littreeset("pot", "pota")));
  assertFalse("potato 4", startsWithOneOf_treeSet("potato", littreeset("potash")));
}