tests: import: Factorize utility function.

* tests/pypi.scm (mock): Move this...
* guix/tests.scm: to here.

guix/tests.scm

@@ -27,6 +27,7 @@ (define-module (guix tests)
   #:export (open-connection-for-tests
             random-text
             random-bytevector
+            mock
             with-derivation-narinfo
             dummy-package))
 
@@ -70,6 +71,16 @@ (define (random-bytevector n)
             (loop (1+ i)))
           bv))))
 
+(define-syntax-rule (mock (module proc replacement) body ...)
+  "Within BODY, replace the definition of PROC from MODULE with the definition
+given by REPLACEMENT."
+  (let* ((m (resolve-module 'module))
+         (original (module-ref m 'proc)))
+    (dynamic-wind
+      (lambda () (module-set! m 'proc replacement))
+      (lambda () body ...)
+      (lambda () (module-set! m 'proc original)))))
+
 
 ;;;
 ;;; Narinfo files, as used by the substituter.

tests/pypi.scm

@@ -20,17 +20,10 @@ (define-module (test-pypi)
   #:use-module (guix import pypi)
   #:use-module (guix base32)
   #:use-module (guix hash)
+  #:use-module (guix tests)
   #:use-module (srfi srfi-64)
   #:use-module (ice-9 match))
 
-(define-syntax-rule (mock (module proc replacement) body ...)
-  (let* ((m (resolve-module 'module))
-         (original (module-ref m 'proc)))
-    (dynamic-wind
-      (lambda () (module-set! m 'proc replacement))
-      (lambda () body ...)
-      (lambda () (module-set! m 'proc original)))))
-
 (define test-json
   "{
   \"info\": {