Testcase for Transitivity of snapshot layers.

Given snapshots A <- B <- C,
B is the parent of C and A is a transitive parent of C

Signed-off-by: Kunal Kushwaha <kushwaha_kunal_v7@lab.ntt.co.jp>

snapshot/snapshotter.go

@@ -219,6 +219,8 @@ func SnapshotterSuite(t *testing.T, name string, snapshotterFn func(root string)
 	t.Run("Basic", makeTest(t, name, snapshotterFn, checkSnapshotterBasic))
 	t.Run("StatActive", makeTest(t, name, snapshotterFn, checkSnapshotterStatActive))
 	t.Run("StatComitted", makeTest(t, name, snapshotterFn, checkSnapshotterStatCommitted))
+	t.Run("TransitivityTest", makeTest(t, name, snapshotterFn, checkSnapshotterTransitivity))
+
 }
 
 func makeTest(t *testing.T, name string, snapshotterFn func(root string) (Snapshotter, func(), error), fn func(t *testing.T, snapshotter Snapshotter, work string)) func(t *testing.T) {

snapshot/testsuite.go

@@ -2,6 +2,7 @@ package snapshot
 
 import (
 	"context"
+	"fmt"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -87,3 +88,79 @@ func checkSnapshotterStatCommitted(t *testing.T, snapshotter Snapshotter, work s
 	assert.Equal(t, "", si.Parent)
 
 }
+
+func snapshotterPrepareMount(ctx context.Context, snapshotter Snapshotter, diffPathName string, parent string, work string) (string, error) {
+	preparing := filepath.Join(work, diffPathName)
+	if err := os.MkdirAll(preparing, 0777); err != nil {
+		return "", err
+	}
+
+	mounts, err := snapshotter.Prepare(ctx, preparing, parent)
+	if err != nil {
+		return "", err
+	}
+
+	if len(mounts) < 1 {
+		return "", fmt.Errorf("expected mounts to have entries")
+	}
+
+	if err = containerd.MountAll(mounts, preparing); err != nil {
+		return "", err
+	}
+	return preparing, nil
+}
+
+// Given A <- B <- C, B is the parent of C and A is a transitive parent of C (in this case, a "grandparent")
+func checkSnapshotterTransitivity(t *testing.T, snapshotter Snapshotter, work string) {
+	ctx := context.TODO()
+	preparing, err := snapshotterPrepareMount(ctx, snapshotter, "preparing", "", work)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer testutil.Unmount(t, preparing)
+
+	if err = ioutil.WriteFile(filepath.Join(preparing, "foo"), []byte("foo\n"), 0777); err != nil {
+		t.Fatal(err)
+	}
+
+	snapA := filepath.Join(work, "snapA")
+	if err = snapshotter.Commit(ctx, snapA, preparing); err != nil {
+		t.Fatal(err)
+	}
+
+	next, err := snapshotterPrepareMount(ctx, snapshotter, "next", snapA, work)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer testutil.Unmount(t, next)
+
+	if err = ioutil.WriteFile(filepath.Join(next, "foo"), []byte("foo bar\n"), 0777); err != nil {
+		t.Fatal(err)
+	}
+
+	snapB := filepath.Join(work, "snapB")
+	if err = snapshotter.Commit(ctx, snapB, next); err != nil {
+		t.Fatal(err)
+	}
+
+	siA, err := snapshotter.Stat(ctx, snapA)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	siB, err := snapshotter.Stat(ctx, snapB)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	siParentB, err := snapshotter.Stat(ctx, siB.Parent)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Test the transivity
+	assert.Equal(t, "", siA.Parent)
+	assert.Equal(t, snapA, siB.Parent)
+	assert.Equal(t, "", siParentB.Parent)
+
+}