Add some tests for the suggestions

src/libutil/suggestions.cc

@@ -5,15 +5,8 @@
 
 namespace nix {
 
-/**
- * Return `some(distance)` where distance is an integer representing some
- * notion of distance between both arguments.
- *
- * If the distance is too big, return none
- */
-int distanceBetween(std::string_view first, std::string_view second)
+int levenshteinDistance(std::string_view first, std::string_view second)
 {
-    // Levenshtein distance.
     // Implementation borrowed from
     // https://en.wikipedia.org/wiki/Levenshtein_distance#Iterative_with_two_matrix_rows
 
@@ -49,7 +42,7 @@ Suggestions Suggestions::bestMatches (
     std::set<Suggestion> res;
     for (const auto & possibleMatch : allMatches) {
         res.insert(Suggestion {
-            .distance = distanceBetween(query, possibleMatch),
+            .distance = levenshteinDistance(query, possibleMatch),
             .suggestion = possibleMatch,
         });
     }
@@ -63,7 +56,7 @@ Suggestions Suggestions::trim(int limit, int maxDistance) const
     int count = 0;
 
     for (auto & elt : suggestions) {
-        if (count >= limit || elt.distance >= maxDistance)
+        if (count >= limit || elt.distance > maxDistance)
             break;
         count++;
         res.insert(elt);

src/libutil/suggestions.hh

@@ -6,6 +6,8 @@
 
 namespace nix {
 
+int levenshteinDistance(std::string_view first, std::string_view second);
+
 /**
  * A potential suggestion for the cli interface.
  */

src/libutil/tests/suggestions.cc

@@ -0,0 +1,43 @@
+#include "suggestions.hh"
+#include <gtest/gtest.h>
+
+namespace nix {
+
+    struct LevenshteinDistanceParam {
+        std::string s1, s2;
+        int distance;
+    };
+
+    class LevenshteinDistanceTest :
+        public testing::TestWithParam<LevenshteinDistanceParam> {
+    };
+
+    TEST_P(LevenshteinDistanceTest, CorrectlyComputed) {
+        auto params = GetParam();
+
+        ASSERT_EQ(levenshteinDistance(params.s1, params.s2), params.distance);
+        ASSERT_EQ(levenshteinDistance(params.s2, params.s1), params.distance);
+    }
+
+    INSTANTIATE_TEST_SUITE_P(LevenshteinDistance, LevenshteinDistanceTest,
+            testing::Values(
+                LevenshteinDistanceParam{"foo", "foo", 0},
+                LevenshteinDistanceParam{"foo", "", 3},
+                LevenshteinDistanceParam{"", "", 0},
+                LevenshteinDistanceParam{"foo", "fo", 1},
+                LevenshteinDistanceParam{"foo", "oo", 1},
+                LevenshteinDistanceParam{"foo", "fao", 1},
+                LevenshteinDistanceParam{"foo", "abc", 3}
+            )
+    );
+
+    TEST(Suggestions, Trim) {
+        auto suggestions = Suggestions::bestMatches({"foooo", "bar", "fo", "gao"}, "foo");
+        auto onlyOne = suggestions.trim(1);
+        ASSERT_EQ(onlyOne.suggestions.size(), 1);
+        ASSERT_TRUE(onlyOne.suggestions.begin()->suggestion == "fo");
+
+        auto closest = suggestions.trim(999, 2);
+        ASSERT_EQ(closest.suggestions.size(), 3);
+    }
+}