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+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2023 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 (guix import test)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:use-module (web uri)
+  #:use-module (guix packages)
+  #:use-module (guix upstream)
+  #:use-module ((guix utils) #:select (version-prefix?))
+  #:use-module (ice-9 vlist)
+  #:use-module (ice-9 match)
+  #:export (%test-updater))
+
+;;; Commentary:
+;;;
+;;; This module defines a pseudo updater whose sole purpose is to allow
+;;; testing of the whole 'guix refresh' command.
+;;;
+;;; Code:
+
+(define test-target-version
+  ;; VHash that maps package names to version/URL tuples.
+  (make-parameter
+   (or (and=> (getenv "GUIX_TEST_UPDATER_TARGETS")
+              (lambda (str)
+                (alist->vhash (call-with-input-string str read))))
+       vlist-null)))
+
+(define (available-updates package)
+  "Return the list of available <upstream-source> records for PACKAGE."
+  (vhash-fold* (lambda (version+updates result)
+                 (match version+updates
+                   ((version (updates ...))
+                    (if (version-prefix? version
+                                         (package-version package))
+                        (append (map (match-lambda
+                                       ((version url)
+                                        (upstream-source
+                                         (package (package-name package))
+                                         (version version)
+                                         (urls (list url)))))
+                                     updates)
+                                result)
+                        result))))
+               '()
+               (package-name package)
+               (test-target-version)))
+
+(define (test-package? package)
+  "Return true if PACKAGE has pseudo updates available."
+  (and (not (vlist-null? (test-target-version)))  ;cheap test
+       (pair? (available-updates package))))
+
+(define* (import-release package #:key (version #f))
+  "Return the <upstream-source> record denoting either the latest version of
+PACKAGE or VERSION."
+  (match (available-updates package)
+    (() #f)
+    ((sources ...)
+     (if version
+         (find (lambda (source)
+                 (string=? (upstream-source-version source)
+                           version))
+               sources)
+         (first sources)))))
+
+(define %test-updater
+  (upstream-updater
+   (name 'test)
+   (description "Pseudo updater for testing purposes.")
+   (pred test-package?)
+   (import import-release)))