Add better test coverage

lib/src/adf.rs

@@ -1137,7 +1137,7 @@ mod test {
             vec![vec![Term(0), Term(1)], vec![Term(1), Term(0)]]
         );
 
-        adf.stable_nogood_channel(Heuristic::Simple, s);
+        adf.stable_nogood_channel(Heuristic::default(), s);
         assert_eq!(
             r.iter().collect::<Vec<_>>(),
             vec![vec![Term(1), Term(0)], vec![Term(0), Term(1)]]

lib/src/adf/heuristics.rs

@@ -121,3 +121,19 @@ impl Heuristic<'_> {
         }
     }
 }
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::datatypes::Term;
+    use crate::datatypes::Var;
+
+    #[test]
+    fn debug_out() {
+        dbg!(Heuristic::Simple);
+        dbg!(Heuristic::MinModMaxVarImpMinPaths);
+        dbg!(Heuristic::MinModMinPathsMaxVarImp);
+        dbg!(Heuristic::Custom(&|_adf: &Adf,
+                                 _int: &[Term]|
+         -> Option<(Var, Term)> { None }));
+    }
+}