Ranking: test sharded search with document ranks (#545)

This adds an integration test for sharded search when document ranking is
enabled. It checks that results are combined correctly across multiple shards,
and that the ranked combined results are streamed out.

shards/shards_test.go

@@ -226,6 +226,66 @@ func TestShardedSearcher_Ranking(t *testing.T) {
 	}
 }
 
+func TestShardedSearcher_DocumentRanking(t *testing.T) {
+	ss := newShardedSearcher(1)
+
+	var nextShardNum int
+	addShard := func(repo string, priority float64, docs ...zoekt.Document) {
+		r := &zoekt.Repository{ID: hash(repo), Name: repo}
+		r.RawConfig = map[string]string{
+			"public":   "1",
+			"priority": strconv.FormatFloat(priority, 'f', 2, 64),
+		}
+		b := testIndexBuilder(t, r, docs...)
+		shard := searcherForTest(t, b)
+		ss.replace(map[string]zoekt.Searcher{
+			fmt.Sprintf("key-%d", nextShardNum): shard,
+		})
+		nextShardNum++
+	}
+
+	addShard("weekend-project", 0.25, zoekt.Document{Name: "f1", Content: []byte("foobar")})
+	addShard("moderately-popular", 0.4, zoekt.Document{Name: "f2", Content: []byte("foobaz")})
+	addShard("weekend-project-2", 0.25, zoekt.Document{Name: "f3", Content: []byte("foo bar")})
+	addShard("super-star", 0.9, zoekt.Document{Name: "f4", Content: []byte("foo baz")},
+		zoekt.Document{Name: "f5", Content: []byte("fooooo")})
+
+	// Run a stream search and gather the results
+	var results []*zoekt.SearchResult
+	opts := &zoekt.SearchOptions{
+		UseDocumentRanks: true,
+		FlushWallTime:    100 * time.Millisecond,
+	}
+
+	err := ss.StreamSearch(context.Background(), &query.Substring{Pattern: "foo"}, opts,
+		stream.SenderFunc(func(event *zoekt.SearchResult) {
+			results = append(results, event)
+		}))
+
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// There should always be two stream results, first progress-only, then the file results
+	if len(results) != 2 {
+		t.Fatalf("expected 2 streamed results, but got %d", len(results))
+	}
+
+	// The ranking should be determined by whether it's an exact word match,
+	// followed by repository priority
+	want := []string{"f4", "f3", "f5", "f2", "f1"}
+
+	files := results[1].Files
+	got := make([]string, len(files))
+	for i := 0; i < len(files); i++ {
+		got[i] = files[i].FileName
+	}
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %v, want %v", got, want)
+	}
+}
+
 func TestFilteringShardsByRepoSetOrBranchesReposOrRepoIDs(t *testing.T) {
 	ss := newShardedSearcher(1)