feat(librarian): add test-container test logic (#2656)

Adding test logic according to
[go/sdk-librarian:container-test](http://goto.google.com/sdk-librarian:container-test).

Tested locally with a couple of libraries in google-cloud-go.
Note: Removed changes for adding the command, will address in separate
PR.

For #2623

Author: zhumin8

go.mod

@@ -11,6 +11,7 @@ require (
 	github.com/go-git/go-git/v5 v5.16.2
 	github.com/google/go-cmp v0.7.0
 	github.com/google/go-github/v69 v69.2.0
+	github.com/google/uuid v1.6.0
 	github.com/googleapis/gax-go/v2 v2.15.0
 	github.com/iancoleman/strcase v0.3.0
 	github.com/pb33f/libopenapi v0.25.9

internal/gitrepo/gitrepo.go

@@ -50,12 +50,16 @@ type Repository interface {
 	GetCommitsForPathsSinceTag(paths []string, tagName string) ([]*Commit, error)
 	GetCommitsForPathsSinceCommit(paths []string, sinceCommit string) ([]*Commit, error)
 	CreateBranchAndCheckout(name string) error
+	CheckoutCommitAndCreateBranch(name, commitHash string) error
+	NewAndDeletedFiles() ([]string, error)
 	Push(branchName string) error
 	Restore(paths []string) error
 	CleanUntracked(paths []string) error
 	pushRefSpec(refSpec string) error
 	Checkout(commitHash string) error
 	GetHashForPath(commitHash, path string) (string, error)
+	ResetHard() error
+	DeleteLocalBranches(names []string) error
 }
 
 const RootPath = "."
@@ -257,6 +261,30 @@ func (r *LocalRepository) ChangedFiles() ([]string, error) {
 	return changedFiles, nil
 }
 
+// NewAndDeletedFiles returns a list of files that are new or deleted.
+func (r *LocalRepository) NewAndDeletedFiles() ([]string, error) {
+	slog.Debug("getting new and deleted files")
+	worktree, err := r.repo.Worktree()
+	if err != nil {
+		return nil, err
+	}
+	status, err := worktree.Status()
+	if err != nil {
+		return nil, err
+	}
+	var files []string
+	for file, fileStatus := range status {
+		switch {
+		case fileStatus.Worktree == git.Untracked,
+			fileStatus.Staging == git.Added,
+			fileStatus.Worktree == git.Deleted,
+			fileStatus.Staging == git.Deleted:
+			files = append(files, file)
+		}
+	}
+	return files, nil
+}
+
 // Remotes returns the remotes within the repository.
 func (r *LocalRepository) Remotes() ([]*Remote, error) {
 	gitRemotes, err := r.repo.Remotes()
@@ -512,6 +540,21 @@ func (r *LocalRepository) CreateBranchAndCheckout(name string) error {
 	})
 }
 
+// CheckoutCommitAndCreateBranch creates a new git branch from a specific commit hash
+// and checks out the branch in the local git repository.
+func (r *LocalRepository) CheckoutCommitAndCreateBranch(name, commitHash string) error {
+	slog.Debug("creating branch from commit and checking out", "name", name, "commit", commitHash)
+	worktree, err := r.repo.Worktree()
+	if err != nil {
+		return err
+	}
+	return worktree.Checkout(&git.CheckoutOptions{
+		Hash:   plumbing.NewHash(commitHash),
+		Branch: plumbing.NewBranchReferenceName(name),
+		Create: true,
+	})
+}
+
 // Push pushes the local branch to the origin remote.
 func (r *LocalRepository) Push(branchName string) error {
 	// https://stackoverflow.com/a/75727620
@@ -683,3 +726,38 @@ func (r *LocalRepository) GetHashForPath(commitHash, path string) (string, error
 	}
 	return getHashForPath(commit, path)
 }
+
+// ResetHard resets the repository to HEAD, discarding all local changes.
+func (r *LocalRepository) ResetHard() error {
+	worktree, err := r.repo.Worktree()
+	if err != nil {
+		return err
+	}
+	return worktree.Reset(&git.ResetOptions{
+		Mode: git.HardReset,
+	})
+}
+
+// DeleteLocalBranches deletes a list of local branches.
+// It returns an error if any branch deletion fails, or nil if all succeed.
+func (r *LocalRepository) DeleteLocalBranches(names []string) error {
+	slog.Debug("starting batch deletion of local branches", "count", len(names))
+	headRef, headErr := r.repo.Head()
+	if headErr != nil && !errors.Is(headErr, plumbing.ErrReferenceNotFound) {
+		return fmt.Errorf("failed to get HEAD to protect against its deletion: %w", headErr)
+	}
+	for _, name := range names {
+		refName := plumbing.NewBranchReferenceName(name)
+		_, err := r.repo.Storer.Reference(refName)
+		if err != nil {
+			return fmt.Errorf("failed to check existence of branch %s: %w", name, err)
+		}
+		if headErr == nil && headRef.Name() == refName {
+			return fmt.Errorf("cannot delete branch %s: it is the currently checked out branch (HEAD)", name)
+		}
+		if err := r.repo.Storer.RemoveReference(refName); err != nil {
+			return fmt.Errorf("failed to delete branch %s: %w", name, err)
+		}
+	}
+	return nil
+}