internal/testgit: Add helpers to prepare for commit testing

1 files changed, 41 insertions, 0 deletions

diff --git a/internal/testgit/tree.go b/internal/testgit/tree.go
new file mode 100644
index 00000000..3f80d1c3
--- /dev/null
+++ b/internal/testgit/tree.go
@@ -0,0 +1,41 @@
+package testgit
+
+import (
+	"bytes"
+	"fmt"
+	"strings"
+	"testing"
+
+	"lindenii.org/go/furgit/object/id"
+	"lindenii.org/go/furgit/object/typ"
+)
+
+// MkTreeEntry is one entry of a tree built by [Repo.MkTree].
+type MkTreeEntry struct {
+	Mode string
+	Type typ.Type
+	OID  id.ObjectID
+	Name string
+}
+
+// MkTree builds a tree object from entries and returns its object ID.
+func (repo *Repo) MkTree(tb testing.TB, entries []MkTreeEntry) (id.ObjectID, error) {
+	tb.Helper()
+
+	var stdin bytes.Buffer
+	for _, entry := range entries {
+		fmt.Fprintf(&stdin, "%s %s %s\t%s\n", entry.Mode, entry.Type.Name(), entry.OID.String(), entry.Name)
+	}
+
+	stdout, err := repo.Run(tb, &stdin, "git", "mktree")
+	if err != nil {
+		return id.ObjectID{}, fmt.Errorf("mktree: %w", err)
+	}
+
+	treeID, err := repo.objectFormat.FromString(strings.TrimSuffix(string(stdout), "\n"))
+	if err != nil {
+		return id.ObjectID{}, fmt.Errorf("parse git mktree output %q: %w", string(stdout), err)
+	}
+
+	return treeID, nil
+}