@Test
public void testBasicFeatures() {
Stack stack = new Stack();
assertTrue(stack.isEmpty());
stack.push("first");
assertFalse(stack.isEmpty());
String peek = stack.peek();
assertThat(peek, is("first"));
assertFalse(stack.isEmpty());
String pop = stack.pop();
assertThat(pop, is("first"));
assertTrue(stack.isEmpty());
}
@Test
public void shouldReturnNullOnEmptyPeak() throws Exception {
Stack stack = new Stack();
String peek = stack.peek();
assertThat(peek, is(nullValue()));
}