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diff --git a/tests/combinators.scm b/tests/combinators.scm
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+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2012, 2013, 2014, 2015, 2016 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2014 Eric Bavier <bavier@member.fsf.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-combinators)
+  #:use-module (guix combinators)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-64)
+  #:use-module (ice-9 vlist))
+
+(test-begin "combinators")
+
+(test-equal "fold2, 1 list"
+    (list (reverse (iota 5))
+          (map - (reverse (iota 5))))
+  (call-with-values
+      (lambda ()
+        (fold2 (lambda (i r1 r2)
+                 (values (cons i r1)
+                         (cons (- i) r2)))
+               '() '()
+               (iota 5)))
+    list))
+
+(test-equal "fold2, 2 lists"
+    (list (reverse '((a . 0) (b . 1) (c . 2) (d . 3)))
+          (reverse '((a . 0) (b . -1) (c . -2) (d . -3))))
+  (call-with-values
+      (lambda ()
+        (fold2 (lambda (k v r1 r2)
+                 (values (alist-cons k v r1)
+                         (alist-cons k (- v) r2)))
+               '() '()
+               '(a b c d)
+               '(0 1 2 3)))
+    list))
+
+(let* ((tree (alist->vhash
+              '((0 2 3) (1 3 4) (2) (3 5 6) (4 6) (5) (6))
+              hashq))
+       (add-one (lambda (_ r) (1+ r)))
+       (tree-lookup (lambda (n) (cdr (vhash-assq n tree)))))
+  (test-equal "fold-tree, single root"
+    5 (fold-tree add-one 0 tree-lookup '(0)))
+  (test-equal "fold-tree, two roots"
+    7 (fold-tree add-one 0 tree-lookup '(0 1)))
+  (test-equal "fold-tree, sum"
+    16 (fold-tree + 0 tree-lookup '(0)))
+  (test-equal "fold-tree, internal"
+    18 (fold-tree + 0 tree-lookup '(3 4)))
+  (test-equal "fold-tree, cons"
+    '(1 3 4 5 6)
+    (sort (fold-tree cons '() tree-lookup '(1)) <))
+  (test-equal "fold-tree, overlapping paths"
+    '(1 3 4 5 6)
+    (sort (fold-tree cons '() tree-lookup '(1 4)) <))
+  (test-equal "fold-tree, cons, two roots"
+    '(0 2 3 4 5 6)
+    (sort (fold-tree cons '() tree-lookup '(0 4)) <))
+  (test-equal "fold-tree-leaves, single root"
+    2 (fold-tree-leaves add-one 0 tree-lookup '(1)))
+  (test-equal "fold-tree-leaves, single root, sum"
+    11 (fold-tree-leaves + 0 tree-lookup '(1)))
+  (test-equal "fold-tree-leaves, two roots"
+    3 (fold-tree-leaves add-one 0 tree-lookup '(0 1)))
+  (test-equal "fold-tree-leaves, two roots, sum"
+    13 (fold-tree-leaves + 0 tree-lookup '(0 1))))
+
+(test-end)
+