Add hy2py tests for empty data structures

tests/resources/pydemo.hy

@@ -29,6 +29,11 @@ Call me Ishmael. Some years ago—never mind how long precisely—having little
 (setv myset #{4 5 6})
 (setv mydict {7 8  9 900  10 15})
 
+(setv emptylist [])
+(setv emptytuple (,))
+(setv emptyset #{})
+(setv emptydict {})
+
 (setv mylistcomp (lfor x (range 10) :if (% x 2) x))
 (setv mysetcomp (sfor x (range 5) :if (not (% x 2)) x))
 (setv mydictcomp (dfor k "abcde" :if (!= k "c") [k (.upper k)]))

tests/test_hy2py.py

@@ -53,6 +53,11 @@ def assert_stuff(m):
     assert m.myset == {4, 5, 6}
     assert m.mydict == {7: 8, 9: 900, 10: 15}
 
+    assert m.emptylist == []
+    assert m.emptytuple == ()
+    assert m.emptyset == set()
+    assert m.emptydict == {}
+
     assert m.mylistcomp == [1, 3, 5, 7, 9]
     assert m.mysetcomp == {0, 2, 4}
     assert m.mydictcomp == dict(a="A", b="B", d="D", e="E")