Add TestLogFileWithError for coverage

Signed-off-by: knqyf263 <knqyf263@gmail.com>

repository_test.go

diff --git a/repository_test.go b/repository_test.go
index 0e46ded..5fc6aeb 100644
--- a/repository_test.go
+++ b/repository_test.go
@@ -3,6 +3,7 @@
 import (
 	"bytes"
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -13,7 +14,6 @@
 	"testing"
 	"time"
 
-
 	"golang.org/x/crypto/openpgp"
 	"golang.org/x/crypto/openpgp/armor"
 	openpgperr "golang.org/x/crypto/openpgp/errors"
@@ -1653,6 +1653,28 @@
 	c.Assert(iterErr, Equals, io.EOF)
 }
 
+type mockErrCommitIter struct{}
+
+func (m *mockErrCommitIter) Next() (*object.Commit, error) {
+	return nil, errors.New("mock next error")
+}
+func (m *mockErrCommitIter) ForEach(func(*object.Commit) error) error {
+	return errors.New("mock foreach error")
+}
+
+func (m *mockErrCommitIter) Close() {}
+
+func (s *RepositorySuite) TestLogFileWithError(c *C) {
+	fileName := "README"
+	cIter := object.NewCommitFileIterFromIter(fileName, &mockErrCommitIter{}, false)
+	defer cIter.Close()
+
+	err := cIter.ForEach(func(commit *object.Commit) error {
+		return nil
+	})
+	c.Assert(err, NotNil)
+}
+
 func (s *RepositorySuite) TestCommit(c *C) {
 	r, _ := Init(memory.NewStorage(), nil)
 	err := r.clone(context.Background(), &CloneOptions{