@Test
public void testFrequency() {

	Vocabulary vocabulary = new Vocabulary();
	vocabulary.add("only one");
	vocabulary.add("we are 2");
	vocabulary.add("we are 2");
	vocabulary.add("I like kitten");
	assertEquals(0.25, vocabulary.frequency("only one"), 0.001);
	assertEquals(0.5, vocabulary.frequency("we are 2"), 0.001);
	assertEquals(0.0, vocabulary.frequency("I'm not here"), 0.001);
}