tests: Move 'file=?' to (guix tests).

* tests/nar.scm (file-tree-equal?)[file=?]: Move to...
* guix/tests.scm (file=?): ... here.  New procedure.

guix/tests.scm

@@ -27,10 +27,12 @@
   #:use-module (gnu packages bootstrap)
   #:use-module (srfi srfi-34)
   #:use-module (rnrs bytevectors)
+  #:use-module (rnrs io ports)
   #:use-module (web uri)
   #:export (open-connection-for-tests
             random-text
             random-bytevector
+            file=?
             network-reachable?
             shebang-too-long?
             mock
@@ -88,6 +90,19 @@
             (loop (1+ i)))
           bv))))
 
+(define (file=? a b)
+  "Return true if files A and B have the same type and same content."
+  (and (eq? (stat:type (lstat a)) (stat:type (lstat b)))
+       (case (stat:type (lstat a))
+         ((regular)
+          (equal?
+           (call-with-input-file a get-bytevector-all)
+           (call-with-input-file b get-bytevector-all)))
+         ((symlink)
+          (string=? (readlink a) (readlink b)))
+         (else
+          (error "what?" (lstat a))))))
+
 (define (network-reachable?)
   "Return true if we can reach the Internet."
   (false-if-exception (getaddrinfo "www.gnu.org" "80" AI_NUMERICSERV)))

tests/nar.scm

@@ -108,17 +108,6 @@
     (cute string-drop <> (string-length input)))
   (define sibling
     (compose (cut string-append output <>) strip))
-  (define (file=? a b)
-    (and (eq? (stat:type (lstat a)) (stat:type (lstat b)))
-         (case (stat:type (lstat a))
-           ((regular)
-            (equal?
-             (call-with-input-file a get-bytevector-all)
-             (call-with-input-file b get-bytevector-all)))
-           ((symlink)
-            (string=? (readlink a) (readlink b)))
-           (else
-            (error "what?" (lstat a))))))
 
   (file-system-fold (const #t)
                     (lambda (name stat result)    ; leaf