### Question:
Columns implements Iterable<Column> { public int count() { return columns.length; } Columns(Column... columns);  Columns(Collection<Column> columns); boolean contains(Column column); boolean contains(Columns columns); Iterator<Column> iterator(); int count(); String namesJoint(String separator); String namesJoint(String template, String separator); Columns exclude(Columns toexclude); @Override int hashCode(); @Override boolean equals(Object obj); @Override String toString();  }### Answer:
@Test public void count_returnsTheNumberOfColumns() { assertEquals(2, new Columns(NAME, BIRTH_DATE).count()); assertEquals(0, new Columns().count()); }