pack: Add unit test.

* guix/scripts/pack.scm (self-contained-tarball): Add #:tar option.
[build](tar-supports-sort?): New variable.  Use it.
* tests/pack.scm: New file.
* Makefile.am (SCM_TESTS): Add it.

Makefile.am

@@ -297,6 +297,7 @@ SCM_TESTS =					\
   tests/services.scm				\
   tests/scripts-build.scm			\
   tests/containers.scm				\
+  tests/pack.scm				\
   tests/import-utils.scm
 
 if HAVE_GUILE_JSON

guix/scripts/pack.scm

@@ -70,7 +70,8 @@ found."
                                  #:key deduplicate?
                                  (compressor (first %compressors))
                                  localstatedir?
-                                 (symlinks '()))
+                                 (symlinks '())
+                                 (tar tar))
   "Return a self-contained tarball containing a store initialized with the
 closure of PROFILE, a derivation.  The tarball contains /gnu/store; if
 LOCALSTATEDIR? is true, it also contains /var/guix, including /var/guix/db
@@ -104,6 +105,14 @@ added to the pack."
             ;; Fully-qualified symlinks.
             (append-map symlink->directives '#$symlinks))
 
+          ;; The --sort option was added to GNU tar in version 1.28, released
+          ;; 2014-07-28.  For testing, we use the bootstrap tar, which is
+          ;; older and doesn't support it.
+          (define tar-supports-sort?
+            (zero? (system* (string-append #+tar "/bin/tar")
+                            "cf" "/dev/null" "--files-from=/dev/null"
+                            "--sort=name")))
+
           ;; We need Guix here for 'guix-register'.
           (setenv "PATH"
                   (string-append #$(if localstatedir?
@@ -137,7 +146,7 @@ added to the pack."
                            ;; mtime = 1, not zero, because that is what the
                            ;; daemon does for files in the store (see the
                            ;; 'mtimeStore' constant in local-store.cc.)
-                           "--sort=name"
+                           (if tar-supports-sort? "--sort=name" "--mtime=@1")
                            "--mtime=@1"           ;for files in /var/guix
                            "--owner=root:0"
                            "--group=root:0"

tests/pack.scm

@@ -0,0 +1,79 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2017 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (test-pack)
+  #:use-module (guix scripts pack)
+  #:use-module (guix store)
+  #:use-module (guix derivations)
+  #:use-module (guix profiles)
+  #:use-module (guix monads)
+  #:use-module (guix grafts)
+  #:use-module (guix tests)
+  #:use-module (guix gexp)
+  #:use-module (gnu packages bootstrap)
+  #:use-module (srfi srfi-64))
+
+(define %store
+  (open-connection-for-tests))
+
+;; Globally disable grafts because they can trigger early builds.
+(%graft? #f)
+
+(define-syntax-rule (test-assertm name exp)
+  (test-assert name
+    (run-with-store %store exp
+                    #:guile-for-build (%guile-for-build))))
+
+(define %gzip-compressor
+  ;; Compressor that uses the bootstrap 'gzip'.
+  ((@ (guix scripts pack) compressor) "gzip"
+   %bootstrap-coreutils&co "gz" '("gzip" "-6n")))
+
+(define %tar-bootstrap %bootstrap-coreutils&co)
+
+
+(test-begin "pack")
+
+(test-assertm "self-contained-tarball"
+  (mlet* %store-monad
+      ((profile (profile-derivation (packages->manifest
+                                     (list %bootstrap-guile))
+                                    #:hooks '()
+                                    #:locales? #f))
+       (tarball (self-contained-tarball "pack" profile
+                                        #:symlinks '(("/bin/Guile"
+                                                      -> "bin/guile"))
+                                        #:compressor %gzip-compressor
+                                        #:tar %tar-bootstrap))
+       (check   (gexp->derivation
+                 "check-tarball"
+                 #~(let ((guile (string-append "." #$profile "/bin")))
+                     (setenv "PATH"
+                             (string-append #$%tar-bootstrap "/bin"))
+                     (system* "tar" "xvf" #$tarball)
+                     (mkdir #$output)
+                     (exit
+                      (and (file-exists? (string-append guile "/guile"))
+                           (string=? (string-append #$%bootstrap-guile "/bin")
+                                     (readlink guile))
+                           (string=? (string-append (string-drop guile 1)
+                                                    "/guile")
+                                     (readlink "bin/Guile"))))))))
+    (built-derivations (list check))))
+
+(test-end)