diff --git a/common.go b/common.go
index 2c06713d..f041c8df 100644
--- a/common.go
+++ b/common.go
@@ -24,6 +24,7 @@
 package span
 
 import (
+	"encoding/base64"
 	"fmt"
 )
 
@@ -45,3 +46,11 @@ type Skip struct {
 func (s Skip) Error() string {
 	return fmt.Sprintf("[skip] %s", s.Reason)
 }
+
+// GenFincID returns a finc.id string consisting of an arbitraty prefix (e.g.
+// "ai"), source id and URL safe record id. No additional checks, sid and rid
+// should not be empty.
+func GenFincID(sid, rid string) string {
+	return fmt.Sprintf("ai-%s-%s", sid,
+		base64.RawURLEncoding.EncodeToString([]byte(rid)))
+}
diff --git a/id_test.go b/common_test.go
similarity index 100%
rename from id_test.go
rename to common_test.go
diff --git a/id.go b/id.go
deleted file mode 100644
index 285be663..00000000
--- a/id.go
+++ /dev/null
@@ -1,14 +0,0 @@
-package span
-
-import (
-	"encoding/base64"
-	"fmt"
-)
-
-// GenFincID returns a finc.id string consisting of an arbitraty prefix (e.g.
-// "ai"), source id and URL safe record id. No additional checks, sid and rid
-// should not be empty.
-func GenFincID(sid, rid string) string {
-	return fmt.Sprintf("ai-%s-%s", sid,
-		base64.RawURLEncoding.EncodeToString([]byte(rid)))
-}