fiddle: Don't overwrite existing fiddle names unintentionally.

fiddle/go/named/named_test.go

 package named
 
 import (
         "fmt"
         "testing"
 
         "go.skia.org/infra/fiddle/go/store"
 
         "github.com/stretchr/testify/assert"
 )
@@ skipping 69 matching lines @@
 
 func TestAdd(t *testing.T) {
         mock := &namedMock{
                 lookup: map[string]string{
                         "star":     "cbb8dee39e9f1576cd97c2d504db8eee",
                         "bad_hash": "cbb8d",
                 },
         }
 
         names := New(mock)
-        err := names.Add("a_good_name", "cbb8dee39e9f1576cd97c2d504db8eee", "user")
+        err := names.Add("a_good_name", "cbb8dee39e9f1576cd97c2d504db8eee", "user", true)
         assert.NoError(t, err)
 
-        err = names.Add("no spaces in names", "cbb8dee39e9f1576cd97c2d504db8eee", "user")
+        err = names.Add("no spaces in names", "cbb8dee39e9f1576cd97c2d504db8eee", "user", true)
         assert.Error(t, err)
 
-        err = names.Add("a_good_name", "cbb8_bash_hash", "user")
+        err = names.Add("a_good_name", "cbb8_bash_hash", "user", true)
         assert.Error(t, err)
+
+        err = names.Add("star", "cbb8dee39e9f1576cd97c2d504db8eee", "user", false)
+        assert.Equal(t, err, DuplicateNameErr)
+
+        err = names.Add("star", "cbb8dee39e9f1576cd97c2d504db8eee", "user", true)
+        assert.NoError(t, err)
 }