@Test public void ensureLetVisitInvokesVisitFilter()
{
Expr e = new Expr( "someFunction" );
Item name = Item.createVariable( "x" );
Ref<Element> seen = new Ref<Element>();
VisitElement v = new VisitLet();
Let l = new Let( name, e );
l.visit( v );
assertSame( l, v.seen.get() );
}