Add some tests for Index

Including making the default :undefined, so the NIF doesn't get
upset. Implementing the Access protocol would require a struct, so we
may or may not want that.

lib/geef/index.ex

@@ -6,13 +6,15 @@ defmodule Geef.Index.Entry do
   vals   = :lists.map(&{&1, [], nil}, keys)
   pairs  = :lists.zip(keys, vals)
 
-  defstruct keys
+  defaults = :lists.map(fn(_) -> :undefined end, keys)
+
+  defstruct :lists.zip(keys, defaults)
 
   def from_record({:geef_index_entry, unquote_splicing(vals)}) do
     %Geef.Index.Entry{unquote_splicing(pairs)}
   end
 
-  def to_record(%Geef.Index.Entry{unquote_splicing(pairs)}) do
+  def to_record(e = %Geef.Index.Entry{unquote_splicing(pairs)}) do
     {:geef_index_entry, unquote_splicing(vals)}
   end
 
@@ -60,6 +62,10 @@ defmodule Geef.Index do
     :geef_index.write(pid)
   end
 
+  def write_tree(pid, repo) do
+    :geef_index.write_tree(pid, repo)
+  end
+
   @spec write!(pid()) :: :ok
   def write!(pid) do
     case write(pid) do

test/index_test.exs

@@ -0,0 +1,44 @@
+defmodule IndexTest do
+  use ExUnit.Case
+  use Geef
+  alias Geef.Index
+  alias Geef.Index.Entry
+  import RepoHelpers
+
+
+  setup do
+    {repo, path} = tmp_bare()
+    Process.link(repo)
+    on_exit(fn -> File.rm_rf!(path) end)
+    {:ok, [repo: repo, path: path]}
+  end
+
+  test "add an entry to the index", meta do
+    repo = meta[:repo]
+
+    content = "This is some text that will go in a file"
+    {:ok, odb} = Repository.odb(repo)
+    {:ok, id} = Odb.write(odb, content, :blob)
+    assert id == Oid.parse("c300118399f01fe52b316061b5d32beb27e0adfd")
+
+    {:ok, idx} = Index.new
+    {now_mega, now_secs, _} = :os.timestamp()
+    time = now_mega * 1000000 + now_secs
+
+    entry = %Geef.Index.Entry{mode: 0o100644, id: id, path: "README", size: byte_size(content), mtime: time}
+    :ok = Index.add(idx, entry)
+
+    {:ok, tree_id} = Index.write_tree(idx, repo)
+    expected = Oid.parse("5a20bbbf65ea75ad4d9f995d179156824ccca3a1")
+    assert tree_id == expected
+
+    {:ok, entry1} = Index.get(idx, "README", 0)
+#    entry2 = idx["README"]
+
+#    assert entry1 == entry2
+    assert entry1.size == byte_size(content)
+
+    Repository.stop(repo)
+  end
+
+end