test: add basic integration tests

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

tests/integration.go

@@ -0,0 +1,30 @@
+package tests
+
+import (
+	"os"
+	"os/exec"
+	"testing"
+
+	"github.com/containerd/continuity/fs/fstest"
+	"github.com/moby/buildkit/util/testutil/integration"
+)
+
+func tmpdir(t *testing.T, appliers ...fstest.Applier) (string, error) {
+	tmpdir := t.TempDir()
+	if err := fstest.Apply(appliers...).Apply(tmpdir); err != nil {
+		return "", err
+	}
+	return tmpdir, nil
+}
+
+func buildxCmd(sb integration.Sandbox, args ...string) *exec.Cmd {
+	if builder := sb.Address(); builder != "" {
+		args = append([]string{"--builder=" + builder}, args...)
+	}
+	cmd := exec.Command("buildx", args...)
+	if context := sb.DockerAddress(); context != "" {
+		cmd.Env = append(os.Environ(), "DOCKER_CONTEXT="+context)
+	}
+
+	return cmd
+}