Test for empty set of provided uris

conjure-go-client/httpclient/internal/rr_selector.go

@@ -18,6 +18,8 @@ import (
 	"math/rand"
 	"net/http"
 	"sync"
+
+	werror "github.com/palantir/witchcraft-go-error"
 )
 
 type roundRobinSelector struct {
@@ -42,6 +44,9 @@ func NewRoundRobinURISelector(nanoClock func() int64) URISelector {
 func (s *roundRobinSelector) Select(uris []string, _ http.Header) ([]string, error) {
 	s.Lock()
 	defer s.Unlock()
+	if len(uris) == 0 {
+		return nil, werror.Error("no valid uris provided to round robin uri-selector")
+	}
 
 	s.updateURIs(uris)
 	s.offset = (s.offset + 1) % len(uris)

conjure-go-client/httpclient/internal/rr_selector_test.go

@@ -19,27 +19,35 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestRoundRobinSelector_Select(t *testing.T) {
-	uris := []string{"uri1", "uri2", "uri3", "uri4", "uri5"}
 	scorer := NewRoundRobinURISelector(func() int64 { return time.Now().UnixNano() })
 
-	const iterations = 100
-	observed := make(map[string]int, iterations)
-	for i := 0; i < iterations; i++ {
-		uri, err := scorer.Select(uris, nil)
-		assert.NoError(t, err)
-		assert.Len(t, uri, 1)
-		observed[uri[0]] = observed[uri[0]] + 1
-	}
-
-	occurences := make([]int, 0, len(observed))
-	for _, count := range observed {
-		occurences = append(occurences, count)
-	}
-
-	for _, v := range occurences {
-		assert.Equal(t, occurences[0], v)
-	}
+	t.Run("round robins across valid connections", func(t *testing.T) {
+		uris := []string{"uri1", "uri2", "uri3", "uri4", "uri5"}
+		const iterations = 100
+		observed := make(map[string]int, iterations)
+		for i := 0; i < iterations; i++ {
+			uri, err := scorer.Select(uris, nil)
+			assert.NoError(t, err)
+			assert.Len(t, uri, 1)
+			observed[uri[0]] = observed[uri[0]] + 1
+		}
+
+		occurences := make([]int, 0, len(observed))
+		for _, count := range observed {
+			occurences = append(occurences, count)
+		}
+
+		for _, v := range occurences {
+			assert.Equal(t, occurences[0], v)
+		}
+	})
+
+	t.Run("erorrs with empty set of provided uris", func(t *testing.T) {
+		_, err := scorer.Select([]string{}, nil)
+		require.Error(t, err)
+	})
 }