Add smoke test for Relation::from_antijoin

This fails on the prior commit.

Author: ecstatic-morse

src/test.rs

@@ -193,3 +193,12 @@ fn leapjoin_from_extend() {
 
     assert_eq!(variable.elements, vec![(2, 2), (2, 4)]);
 }
+
+#[test]
+fn relation_antijoin_smoke() {
+    let include = Relation::from(vec![("a", "b")]);
+    let exclude = Relation::from(vec![]);
+
+    let output = Relation::from_antijoin(&include, &exclude, |&a, &b| (a, b));
+    assert_eq!(&output[..], &[("a", "b")]);
+}