accounts: return consistent error for duplicate label

accounts/errors.go

@@ -0,0 +1,11 @@
+package accounts
+
+import "errors"
+
+var (
+	// ErrLabelAlreadyExists is returned by the CreateAccount method if the
+	// account label is already used by an existing account.
+	ErrLabelAlreadyExists = errors.New(
+		"account label uniqueness constraint violation",
+	)
+)

accounts/store_kvdb.go

@@ -133,7 +133,8 @@ func (s *BoltStore) NewAccount(ctx context.Context, balance lnwire.MilliSatoshi,
 		for _, account := range accounts {
 			if account.Label == label {
 				return nil, fmt.Errorf("an account with the "+
-					"label '%s' already exists", label)
+					"label '%s' already exists: %w", label,
+					ErrLabelAlreadyExists)
 			}
 		}
 	}

accounts/store_test.go

@@ -29,7 +29,7 @@ func TestAccountStore(t *testing.T) {
 
 	// Make sure we cannot create a second account with the same label.
 	_, err = store.NewAccount(ctx, 123, time.Time{}, "foo")
-	require.ErrorContains(t, err, "account with the label 'foo' already")
+	require.ErrorIs(t, err, ErrLabelAlreadyExists)
 
 	// Make sure we cannot set a label that looks like an account ID.
 	_, err = store.NewAccount(ctx, 123, time.Time{}, "0011223344556677")