Pull from one ChunkStore to another

This initial implementation requires that both the "remote" and local
ChunkStores be accessible by the machine running the pull command.
I took an initial pass at splitting up the functions so that, e.g.,
calculating which refs are needed could be done on an actual remote
machine, and we can add a chunk copying routine that gets data from
the network or something.

Towards issue #81

sync/pull_test.go

@@ -0,0 +1,60 @@
+package sync
+
+import (
+	"testing"
+
+	"github.com/attic-labs/noms/chunks"
+	"github.com/attic-labs/noms/datas"
+	"github.com/attic-labs/noms/dataset"
+	"github.com/attic-labs/noms/types"
+	"github.com/stretchr/testify/assert"
+)
+
+func createTestDataset(name string) dataset.Dataset {
+	var t chunks.ChunkStore = &chunks.TestStore{}
+	return dataset.NewDataset(datas.NewDataStore(t, t.(chunks.RootTracker)), name)
+
+}
+
+func TestValidateRef(t *testing.T) {
+	cs := &chunks.TestStore{}
+	r, err := types.WriteValue(types.Bool(true), cs)
+	assert.NoError(t, err)
+
+	_, err = validateRefAsSetOfCommit(r, cs)
+	assert.Error(t, err)
+}
+
+func TestPull(t *testing.T) {
+	assert := assert.New(t)
+
+	puller := createTestDataset("puller")
+	pullee := createTestDataset("pullee")
+
+	commitValue := func(v types.Value, ds dataset.Dataset) dataset.Dataset {
+		return ds.Commit(
+			datas.NewSetOfCommit().Insert(
+				datas.NewCommit().SetParents(ds.Heads().NomsValue()).SetValue(v)))
+	}
+
+	initialValue := types.NewMap(
+		types.NewString("first"), types.NewList(),
+		types.NewString("second"), types.NewList(types.Int32(2)))
+
+	pullee = commitValue(initialValue, pullee)
+	puller = commitValue(initialValue, puller)
+
+	updatedValue := initialValue.Set(
+		types.NewString("third"), types.NewList(types.Int32(1)))
+
+	pullee = commitValue(updatedValue, pullee)
+
+	refs, err := DiffHeadsByRef(puller.Heads().Ref(), pullee.Heads().Ref(), pullee)
+	assert.NoError(err)
+	assert.NoError(CopyChunks(refs, pullee, puller))
+	puller, err = SetNewHeads(pullee.Heads().Ref(), puller)
+	assert.NoError(err)
+	assert.Equal(pullee.Heads().Ref(), puller.Heads().Ref())
+	assert.True(pullee.Heads().Equals(puller.Heads()))
+
+}