services: configuration: Add tests.

* tests/services/configuration.scm: New file.
* Makefile.am (SCM_TESTS): Register it.

Makefile.am

@@ -484,6 +484,7 @@ SCM_TESTS =					\
   tests/search-paths.scm			\
   tests/services.scm				\
   tests/services/file-sharing.scm		\
+  tests/services/configuration.scm		\
   tests/services/linux.scm			\
   tests/sets.scm				\
   tests/size.scm				\

tests/services/configuration.scm

@@ -0,0 +1,83 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2021 Maxim Cournoyer <maxim.cournoyer@gmail.com>
+;;;
+;;; 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 (tests services linux)
+  #:use-module (gnu services configuration)
+  #:use-module (guix gexp)
+  #:use-module (srfi srfi-34)
+  #:use-module (srfi srfi-64))
+
+;;; Tests for the (gnu services configuration) module.
+
+(test-begin "services-configuration")
+
+
+;;;
+;;; define-configuration macro.
+;;;
+
+(define-configuration port-configuration
+  (port (number 80) "The port number.")
+  (no-serialization))
+
+(test-equal "default value, no serialization"
+  80
+  (port-configuration-port (port-configuration)))
+
+(define-configuration port-configuration-cs
+  (port (number 80) "The port number." empty-serializer))
+
+(test-equal "default value, custom serializer"
+  80
+  (port-configuration-cs-port (port-configuration-cs)))
+
+(define serialize-number "")
+(define-configuration port-configuration-ndv
+  (port (number) "The port number."))
+
+(test-equal "no default value, provided"
+  55
+  (port-configuration-ndv-port (port-configuration-ndv
+                                (port 55))))
+
+(test-assert "no default value, not provided"
+  (guard (c ((configuration-error? c)
+             #t))
+    (port-configuration-ndv-port (port-configuration-ndv))))
+
+(define (custom-number-serializer name value)
+  (format #t "~a = ~a;" name value))
+
+(define-configuration serializable-configuration
+  (port (number 80) "The port number." custom-number-serializer))
+
+(test-assert "serialize-configuration"
+  (gexp?
+   (let ((config (serializable-configuration)))
+     (serialize-configuration config serializable-configuration-fields))))
+
+(define-configuration serializable-configuration
+  (port (number 80) "The port number." custom-number-serializer)
+  (no-serialization))
+
+(test-assert "serialize-configuration with no-serialization"
+  ;; When serialization is disabled, the serializer is set to #f, so
+  ;; attempting to use it fails with a 'wrong-type-arg' error.
+  (not (false-if-exception
+        (let ((config (serializable-configuration)))
+          (serialize-configuration config serializable-configuration-fields)))))