Fix tests after "use new main branch"

Tests worked fine if init.defaultBranch main was used,
but failed due to git branch reasons if master was still used.

Since we can only use init.defaultBranch if git version >= 2.28,
I also went with a template dir HEAD main tweak if lower so tests
now pass regardless of client git default branch and version.

Test: Ran tests with ~/.gitconfig:init.defaultBranch=master
Test: Ran tests with ~/.gitconfig:init.defaultBranch=main
Test: Ran tests for both code branches of git require

Change-Id: I49fa1e4ae45b8aec16a093132ee9fa466cbc11ec
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/290404
Tested-by: Fredrik de Groot <fredrik.de.groot@volvocars.com>
Reviewed-by: Mike Frysinger <vapier@google.com>

tests/test_project.py

@@ -26,6 +26,7 @@ import tempfile
 import unittest
 
 import error
+import git_command
 import git_config
 import platform_utils
 import project
@@ -38,7 +39,19 @@ def TempGitTree():
   # Python 2 support entirely.
   try:
     tempdir = tempfile.mkdtemp(prefix='repo-tests')
-    subprocess.check_call(['git', 'init'], cwd=tempdir)
+
+    # Tests need to assume, that main is default branch at init,
+    # which is not supported in config until 2.28.
+    cmd = ['git', 'init']
+    if git_command.git_require((2, 28, 0)):
+      cmd += ['--initial-branch=main']
+    else:
+      # Use template dir for init.
+      templatedir = tempfile.mkdtemp(prefix='.test-template')
+      with open(os.path.join(templatedir, 'HEAD'), 'w') as fp:
+        fp.write('ref: refs/heads/main\n')
+      cmd += ['--template=', templatedir]
+    subprocess.check_call(cmd, cwd=tempdir)
     yield tempdir
   finally:
     platform_utils.rmtree(tempdir)

tests/test_wrapper.py

@@ -25,6 +25,7 @@ import shutil
 import tempfile
 import unittest
 
+import git_command
 import platform_utils
 from pyversion import is_python3
 import wrapper
@@ -357,7 +358,19 @@ class GitCheckoutTestCase(RepoWrapperTestCase):
 
     remote = os.path.join(cls.GIT_DIR, 'remote')
     os.mkdir(remote)
-    run_git('init', cwd=remote)
+
+    # Tests need to assume, that main is default branch at init,
+    # which is not supported in config until 2.28.
+    if git_command.git_require((2, 28, 0)):
+      initstr = '--initial-branch=main'
+    else:
+      # Use template dir for init.
+      templatedir = tempfile.mkdtemp(prefix='.test-template')
+      with open(os.path.join(templatedir, 'HEAD'), 'w') as fp:
+        fp.write('ref: refs/heads/main\n')
+      initstr = '--template=' + templatedir
+
+    run_git('init', initstr, cwd=remote)
     run_git('commit', '--allow-empty', '-minit', cwd=remote)
     run_git('branch', 'stable', cwd=remote)
     run_git('tag', 'v1.0', cwd=remote)