test: add basic integration tests

Signed-off-by: Justin Chadwell <me@jedevc.com>

vendor/github.com/containerd/continuity/README.md

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+# continuity
+
+[![Go Reference](https://pkg.go.dev/badge/github.com/containerd/continuity.svg)](https://pkg.go.dev/github.com/containerd/continuity)
+[![Build Status](https://github.com/containerd/continuity/workflows/Continuity/badge.svg)](https://github.com/containerd/continuity/actions?query=workflow%3AContinuity+branch%3Amain)
+
+A transport-agnostic, filesystem metadata manifest system
+
+This project is a staging area for experiments in providing transport agnostic
+metadata storage.
+
+See [opencontainers/runtime-spec#11](https://github.com/opencontainers/runtime-spec/issues/11)
+for more details.
+
+## Manifest Format
+
+A continuity manifest encodes filesystem metadata in Protocol Buffers.
+Refer to [proto/manifest.proto](proto/manifest.proto) for more details.
+
+## Usage
+
+Build:
+
+```console
+$ make
+```
+
+Create a manifest (of this repo itself):
+
+```console
+$ ./bin/continuity build . > /tmp/a.pb
+```
+
+Dump a manifest:
+
+```console
+$ ./bin/continuity ls /tmp/a.pb
+...
+-rw-rw-r--      270 B   /.gitignore
+-rw-rw-r--      88 B    /.mailmap
+-rw-rw-r--      187 B   /.travis.yml
+-rw-rw-r--      359 B   /AUTHORS
+-rw-rw-r--      11 kB   /LICENSE
+-rw-rw-r--      1.5 kB  /Makefile
+...
+-rw-rw-r--      986 B   /testutil_test.go
+drwxrwxr-x      0 B     /version
+-rw-rw-r--      478 B   /version/version.go
+```
+
+Verify a manifest:
+
+```console
+$ ./bin/continuity verify . /tmp/a.pb
+```
+
+Break the directory and restore using the manifest:
+```console
+$ chmod 777 Makefile
+$ ./bin/continuity verify . /tmp/a.pb
+2017/06/23 08:00:34 error verifying manifest: resource "/Makefile" has incorrect mode: -rwxrwxrwx != -rw-rw-r--
+$ ./bin/continuity apply . /tmp/a.pb
+$ stat -c %a Makefile
+664
+$ ./bin/continuity verify . /tmp/a.pb
+```
+
+## Platforms
+
+continuity primarily targets Linux. Continuity may compile for and work on
+other operating systems, but those platforms are not tested.
+
+## Contribution Guide
+### Building Proto Package
+
+If you change the proto file you will need to rebuild the generated Go with `go generate`.
+
+```console
+$ go generate ./proto
+```
+
+## Project details
+
+continuity is a containerd sub-project, licensed under the [Apache 2.0 license](./LICENSE).
+As a containerd sub-project, you will find the:
+ * [Project governance](https://github.com/containerd/project/blob/main/GOVERNANCE.md),
+ * [Maintainers](https://github.com/containerd/project/blob/main/MAINTAINERS),
+ * and [Contributing guidelines](https://github.com/containerd/project/blob/main/CONTRIBUTING.md)
+
+information in our [`containerd/project`](https://github.com/containerd/project) repository.