Optimize sync_test.go: eliminate redundant git init calls

- Add setupGitRepo(), setupGitRepoWithBranch(), and setupMinimalGitRepo() helpers
- Refactor 19 test functions to use shared git repo setup
- Reduces duplicate git initialization boilerplate by ~300 lines
- All tests pass with improved maintainability

Related to bd-ktng

cmd/bd/test_wait_helper.go

@@ -1,6 +1,8 @@
 package main
 
 import (
+	"os"
+	"os/exec"
 	"testing"
 	"time"
 )
@@ -18,3 +20,122 @@ func waitFor(t *testing.T, timeout, poll time.Duration, pred func() bool) {
 	}
 	t.Fatalf("condition not met within %v", timeout)
 }
+
+// setupGitRepo creates a temporary git repository and returns its path and cleanup function.
+// The repo is initialized with git config and an initial commit.
+// The current directory is changed to the new repo.
+func setupGitRepo(t *testing.T) (repoPath string, cleanup func()) {
+	t.Helper()
+
+	tmpDir := t.TempDir()
+	originalWd, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("failed to get working directory: %v", err)
+	}
+
+	if err := os.Chdir(tmpDir); err != nil {
+		t.Fatalf("failed to change to temp directory: %v", err)
+	}
+
+	// Initialize git repo
+	if err := exec.Command("git", "init").Run(); err != nil {
+		os.Chdir(originalWd)
+		t.Fatalf("failed to init git repo: %v", err)
+	}
+
+	// Configure git
+	exec.Command("git", "config", "user.email", "test@test.com").Run()
+	exec.Command("git", "config", "user.name", "Test User").Run()
+
+	// Create initial commit
+	if err := os.WriteFile("test.txt", []byte("test"), 0644); err != nil {
+		os.Chdir(originalWd)
+		t.Fatalf("failed to write test file: %v", err)
+	}
+	exec.Command("git", "add", "test.txt").Run()
+	if err := exec.Command("git", "commit", "-m", "initial").Run(); err != nil {
+		os.Chdir(originalWd)
+		t.Fatalf("failed to create initial commit: %v", err)
+	}
+
+	cleanup = func() {
+		os.Chdir(originalWd)
+	}
+
+	return tmpDir, cleanup
+}
+
+// setupGitRepoWithBranch creates a git repo and checks out a specific branch.
+// Use this when tests need a specific branch name (e.g., "main").
+func setupGitRepoWithBranch(t *testing.T, branch string) (repoPath string, cleanup func()) {
+	t.Helper()
+
+	tmpDir := t.TempDir()
+	originalWd, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("failed to get working directory: %v", err)
+	}
+
+	if err := os.Chdir(tmpDir); err != nil {
+		t.Fatalf("failed to change to temp directory: %v", err)
+	}
+
+	// Initialize git repo with specific branch
+	if err := exec.Command("git", "init", "-b", branch).Run(); err != nil {
+		os.Chdir(originalWd)
+		t.Fatalf("failed to init git repo: %v", err)
+	}
+
+	// Configure git
+	exec.Command("git", "config", "user.email", "test@test.com").Run()
+	exec.Command("git", "config", "user.name", "Test User").Run()
+
+	// Create initial commit
+	if err := os.WriteFile("test.txt", []byte("test"), 0644); err != nil {
+		os.Chdir(originalWd)
+		t.Fatalf("failed to write test file: %v", err)
+	}
+	exec.Command("git", "add", "test.txt").Run()
+	if err := exec.Command("git", "commit", "-m", "initial").Run(); err != nil {
+		os.Chdir(originalWd)
+		t.Fatalf("failed to create initial commit: %v", err)
+	}
+
+	cleanup = func() {
+		os.Chdir(originalWd)
+	}
+
+	return tmpDir, cleanup
+}
+
+// setupMinimalGitRepo creates a git repo without an initial commit.
+// Use this when tests need to control the initial state more precisely.
+func setupMinimalGitRepo(t *testing.T) (repoPath string, cleanup func()) {
+	t.Helper()
+
+	tmpDir := t.TempDir()
+	originalWd, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("failed to get working directory: %v", err)
+	}
+
+	if err := os.Chdir(tmpDir); err != nil {
+		t.Fatalf("failed to change to temp directory: %v", err)
+	}
+
+	// Initialize git repo
+	if err := exec.Command("git", "init").Run(); err != nil {
+		os.Chdir(originalWd)
+		t.Fatalf("failed to init git repo: %v", err)
+	}
+
+	// Configure git
+	exec.Command("git", "config", "user.email", "test@test.com").Run()
+	exec.Command("git", "config", "user.name", "Test User").Run()
+
+	cleanup = func() {
+		os.Chdir(originalWd)
+	}
+
+	return tmpDir, cleanup
+}