diff --git a/src/github.com/matrix-org/dendrite/common/test/slice.go b/src/github.com/matrix-org/dendrite/common/test/slice.go
new file mode 100644
index 00000000..00c740db
--- /dev/null
+++ b/src/github.com/matrix-org/dendrite/common/test/slice.go
@@ -0,0 +1,34 @@
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package test
+
+import "sort"
+
+// UnsortedStringSliceEqual returns true if the slices have same length & elements.
+// Does not modify the given slice.
+func UnsortedStringSliceEqual(first, second []string) bool {
+	if len(first) != len(second) {
+		return false
+	}
+
+	a, b := first[:], second[:]
+	sort.Strings(a)
+	sort.Strings(b)
+	for i := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+
+	return true
+}
diff --git a/src/github.com/matrix-org/dendrite/roomserver/query/query_test.go b/src/github.com/matrix-org/dendrite/roomserver/query/query_test.go
index 45e46f67..76c2e158 100644
--- a/src/github.com/matrix-org/dendrite/roomserver/query/query_test.go
+++ b/src/github.com/matrix-org/dendrite/roomserver/query/query_test.go
@@ -19,8 +19,7 @@ import (
 	"encoding/json"
 	"testing"
 
-	"sort"
-
+	"github.com/matrix-org/dendrite/common/test"
 	"github.com/matrix-org/dendrite/roomserver/types"
 	"github.com/matrix-org/gomatrixserverlib"
 )
@@ -90,24 +89,6 @@ func (db *getEventDB) EventsFromIDs(ctx context.Context, eventIDs []string) (res
 	return
 }
 
-// Returns if the slices are equal after sorting them.
-func compareUnsortedStringSlices(a []string, b []string) bool {
-	if len(a) != len(b) {
-		return false
-	}
-
-	sort.Strings(a)
-	sort.Strings(b)
-
-	for i := range a {
-		if a[i] != b[i] {
-			return false
-		}
-	}
-
-	return true
-}
-
 func TestGetAuthChainSingle(t *testing.T) {
 	db := createEventDB()
 
@@ -135,7 +116,7 @@ func TestGetAuthChainSingle(t *testing.T) {
 
 	expectedIDs := []string{"a", "b", "c", "d", "e"}
 
-	if !compareUnsortedStringSlices(expectedIDs, returnedIDs) {
+	if !test.UnsortedStringSliceEqual(expectedIDs, returnedIDs) {
 		t.Fatalf("returnedIDs got '%v', expected '%v'", returnedIDs, expectedIDs)
 	}
 }
@@ -168,7 +149,7 @@ func TestGetAuthChainMultiple(t *testing.T) {
 
 	expectedIDs := []string{"a", "b", "c", "d", "e", "f"}
 
-	if !compareUnsortedStringSlices(expectedIDs, returnedIDs) {
+	if !test.UnsortedStringSliceEqual(expectedIDs, returnedIDs) {
 		t.Fatalf("returnedIDs got '%v', expected '%v'", returnedIDs, expectedIDs)
 	}
 }