Fix for bad commitID to show up in error (#148)

* Fix for bad commitID to show up in error

* Adds test for repo_commit GetCommit

* Adds test if commitID is valid branch

repo_commit.go

@@ -153,13 +153,14 @@ func (repo *Repository) getCommit(id SHA1) (*Commit, error) {
 func (repo *Repository) GetCommit(commitID string) (*Commit, error) {
 	if len(commitID) != 40 {
 		var err error
-		commitID, err = NewCommand("rev-parse", commitID).RunInDir(repo.Path)
+		actualCommitID, err := NewCommand("rev-parse", commitID).RunInDir(repo.Path)
 		if err != nil {
 			if strings.Contains(err.Error(), "unknown revision or path") {
 				return nil, ErrNotExist{commitID, ""}
 			}
 			return nil, err
 		}
+		commitID = actualCommitID
 	}
 	id, err := NewIDFromString(commitID)
 	if err != nil {

repo_commit_test.go

@@ -26,6 +26,7 @@ func TestRepository_GetCommitBranches(t *testing.T) {
 		{"37991dec2c8e592043f47155ce4808d4580f9123", []string{"master"}},
 		{"95bb4d39648ee7e325106df01a621c530863a653", []string{"branch1", "branch2"}},
 		{"8d92fc957a4d7cfd98bc375f0b7bb189a0d6c9f2", []string{"branch2", "master"}},
+		{"master", []string{"master"}},
 	}
 	for _, testCase := range testCases {
 		commit, err := bareRepo1.GetCommit(testCase.CommitID)
@@ -47,3 +48,12 @@ func TestGetTagCommitWithSignature(t *testing.T) {
 	// test that signature is not in message
 	assert.Equal(t, "tag", commit.CommitMessage)
 }
+
+func TestGetCommitWithBadCommitID(t *testing.T) {
+	bareRepo1Path := filepath.Join(testReposDir, "repo1_bare")
+	bareRepo1, err := OpenRepository(bareRepo1Path)
+	commit, err := bareRepo1.GetCommit("bad_branch")
+	assert.Nil(t, commit)
+	assert.Error(t, err)
+	assert.EqualError(t, err, "object does not exist [id: bad_branch, rel_path: ]")
+}