Add some unit tests for find_best_match_for_name

There were only some UI tests that covered this function.
Since there's more diagnostic work going on, I think it makes
sense to have this unit tested.

src/libsyntax/util/lev_distance.rs

@@ -11,7 +11,7 @@
 use std::cmp;
 use symbol::Symbol;
 
-/// To find the Levenshtein distance between two strings
+/// Find the Levenshtein distance between two strings
 pub fn lev_distance(a: &str, b: &str) -> usize {
     // cases which don't require further computation
     if a.is_empty() {
@@ -41,10 +41,12 @@ pub fn lev_distance(a: &str, b: &str) -> usize {
     } dcol[t_last + 1]
 }
 
-/// To find the best match for a given string from an iterator of names
+/// Find the best match for a given word in the given iterator
+///
 /// As a loose rule to avoid the obviously incorrect suggestions, it takes
 /// an optional limit for the maximum allowable edit distance, which defaults
 /// to one-third of the given word.
+///
 /// Besides Levenshtein, we use case insensitive comparison to improve accuracy on an edge case with
 /// a lower(upper)case letters mismatch.
 pub fn find_best_match_for_name<'a, T>(iter_names: T,
@@ -105,3 +107,39 @@ fn test_lev_distance() {
     assert_eq!(lev_distance(b, c), 1);
     assert_eq!(lev_distance(c, b), 1);
 }
+
+#[test]
+fn test_find_best_match_for_name() {
+    use with_globals;
+    with_globals(|| {
+        let input = vec![Symbol::intern("aaab"), Symbol::intern("aaabc")];
+        assert_eq!(
+            find_best_match_for_name(input.iter(), "aaaa", None),
+            Some(Symbol::intern("aaab"))
+        );
+
+        assert_eq!(
+            find_best_match_for_name(input.iter(), "1111111111", None),
+            None
+        );
+
+        let input = vec![Symbol::intern("aAAA")];
+        assert_eq!(
+            find_best_match_for_name(input.iter(), "AAAA", None),
+            Some(Symbol::intern("aAAA"))
+        );
+
+        let input = vec![Symbol::intern("AAAA")];
+        // Returns None because `lev_distance > max_dist / 3`
+        assert_eq!(
+            find_best_match_for_name(input.iter(), "aaaa", None),
+            None
+        );
+
+        let input = vec![Symbol::intern("AAAA")];
+        assert_eq!(
+            find_best_match_for_name(input.iter(), "aaaa", Some(4)),
+            Some(Symbol::intern("AAAA"))
+        );
+    })
+}