When starting an anonymous transaction then original branch is unchanged

src/main/java/net/kemitix/gitdb/GitDBBranch.java

@@ -92,4 +92,11 @@ public interface GitDBBranch {
      * @return the branch name
      */
     String name();
+
+    /**
+     * Gets the commit id for the head of the branch.
+     *
+     * @return an Object Id.
+     */
+    String getCommitId();
 }

src/main/java/net/kemitix/gitdb/impl/GitDBBranchImpl.java

@@ -126,6 +126,11 @@ class GitDBBranchImpl implements GitDBBranch {
         return name;
     }
 
+    @Override
+    public String getCommitId() {
+        return branchRef.getObjectId().name();
+    }
+
     private String commitMessageForAdd(final String key, final String value) {
         return String.format("Add key [%s] = [%s]", key, value);
     }

src/main/java/net/kemitix/gitdb/impl/GitDBTransactionImpl.java

@@ -76,4 +76,9 @@ class GitDBTransactionImpl implements GitDBTransaction {
     public String name() {
         return branch.name();
     }
+
+    @Override
+    public String getCommitId() {
+        return null;
+    }
 }

src/test/java/net/kemitix/gitdb/test/GitDBTest.java

@@ -339,6 +339,20 @@ class GitDBTest implements WithAssertions {
         assertThat(transaction.name()).isNotNull();
     }
 
+    // When starting an anonymous transaction then original branch is unchanged
+    @Test
+    void startAnonymousTransaction_thenOriginalBranchUnchanged() throws IOException {
+        //given
+        final GitDB gitDB = gitDB(dirDoesNotExist());
+        final GitDBBranch gitDBBranch = gitDB.branch("master").get();
+        final String commitId = gitDBBranch.getCommitId();
+        //when
+        final GitDBTransaction transaction = gitDBBranch.transaction();
+        //then
+        assertThat(gitDBBranch.getCommitId()).isEqualTo(commitId);
+        assertThat(gitDB.branch("master").map(GitDBBranch::getCommitId)).contains(commitId);
+    }
+
     // Given a GitDbTransaction handle (i.e. a new branch)
     // When putting a new key/value pair then the original GitDbBranch can't find it
     @Test