Enhance RepositoryTestCase.commitFile() to work on empty repository

Change-Id: Ic64497f0eedf8996ba593ca52dc9a040732a5b24
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/RepositoryTestCase.java

@@ -463,16 +463,25 @@ public abstract class RepositoryTestCase extends LocalDiskRepositoryTestCase {
 	protected RevCommit commitFile(String filename, String contents, String branch) {
 		try {
 			Git git = new Git(db);
-			String originalBranch = git.getRepository().getFullBranch();
-			if (git.getRepository().getRef(branch) == null)
+			Repository repo = git.getRepository();
+			String originalBranch = repo.getFullBranch();
+			boolean empty = repo.resolve(Constants.HEAD) == null;
+			if (!empty) {
+				if (repo.getRef(branch) == null)
 					git.branchCreate().setName(branch).call();
 				git.checkout().setName(branch).call();
+			}
+
 			writeTrashFile(filename, contents);
 			git.add().addFilepattern(filename).call();
 			RevCommit commit = git.commit()
 					.setMessage(branch + ": " + filename).call();
+
 			if (originalBranch != null)
 				git.checkout().setName(originalBranch).call();
+			else if (empty)
+				git.branchCreate().setName(branch).setStartPoint(commit).call();
+
 			return commit;
 		} catch (IOException e) {
 			throw new RuntimeException(e);