remove pkg/testutil/loopback_linux.go and use continuity/testutil/loopback

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

mount/lookup_linux_test.go

@@ -16,14 +16,7 @@
    limitations under the License.
 */
 
-// FIXME: we can't put this test to the mount package:
-// import cycle not allowed in test
-// package github.com/containerd/containerd/mount (test)
-//         imports github.com/containerd/containerd/pkg/testutil
-//         imports github.com/containerd/containerd/mount
-//
-// NOTE: we can't have this as lookup_test (compilation fails)
-package lookuptest
+package mount
 
 import (
 	"fmt"
@@ -34,14 +27,16 @@ import (
 	"strings"
 	"testing"
 
-	"github.com/containerd/containerd/mount"
-	"github.com/containerd/containerd/pkg/testutil"
+	// containerd/pkg/testutil has circular dependency on this mount pkg.
+	// so we use continuity/testutil instead.
+	"github.com/containerd/continuity/testutil"
+	"github.com/containerd/continuity/testutil/loopback"
 	"gotest.tools/assert"
 )
 
 func checkLookup(t *testing.T, fsType, mntPoint, dir string) {
 	t.Helper()
-	info, err := mount.Lookup(dir)
+	info, err := Lookup(dir)
 	assert.NilError(t, err)
 	assert.Equal(t, fsType, info.FSType)
 	assert.Equal(t, mntPoint, info.Mountpoint)
@@ -55,7 +50,7 @@ func testLookup(t *testing.T, fsType string) {
 	}
 	defer os.RemoveAll(mnt)
 
-	deviceName, cleanupDevice, err := testutil.NewLoopback(100 << 20) // 100 MB
+	deviceName, cleanupDevice, err := loopback.New(100 << 20) // 100 MB
 	if err != nil {
 		t.Fatal(err)
 	}

mount/lookup_test/dummy.go

@@ -1,19 +0,0 @@
-/*
-   Copyright The containerd Authors.
-
-   Licensed under the Apache License, Version 2.0 (the "License");
-   you may not use this file except in compliance with the License.
-   You may obtain a copy of the License at
-
-       http://www.apache.org/licenses/LICENSE-2.0
-
-   Unless required by applicable law or agreed to in writing, software
-   distributed under the License is distributed on an "AS IS" BASIS,
-   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-   See the License for the specific language governing permissions and
-   limitations under the License.
-*/
-
-package lookuptest
-
-// FIXME: without this dummy file, `make build` fails with "no buildable Go source files" error