diff --git a/gnu/local.mk b/gnu/local.mk
index 52a021c2a3..d131dc0388 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -692,6 +692,7 @@ GNU_SYSTEM_MODULES =				\
   %D%/tests/desktop.scm				\
   %D%/tests/dict.scm				\
   %D%/tests/docker.scm				\
+  %D%/tests/file-sharing.scm			\
   %D%/tests/ganeti.scm				\
   %D%/tests/guix.scm				\
   %D%/tests/monitoring.scm                      \
diff --git a/gnu/tests/file-sharing.scm b/gnu/tests/file-sharing.scm
new file mode 100644
index 0000000000..9a8ee6a593
--- /dev/null
+++ b/gnu/tests/file-sharing.scm
@@ -0,0 +1,271 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2021 Simon South <simon@simonsouth.net>
+;;;
+;;; 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/>.
+
+;;;
+;;; The Transmission Daemon service.
+;;;
+
+(define-module (gnu tests file-sharing)
+  #:use-module (gnu packages bittorrent)
+  #:use-module (gnu services)
+  #:use-module (gnu services file-sharing)
+  #:use-module (gnu services networking)
+  #:use-module (gnu system vm)
+  #:use-module (gnu tests)
+  #:use-module (guix gexp)
+  #:export (%test-transmission-daemon))
+
+(define %transmission-daemon-user "transmission")
+(define %transmission-daemon-group "transmission")
+
+(define %transmission-daemon-config-dir "/var/lib/transmission-daemon")
+(define %transmission-daemon-watch-dir
+  (string-append %transmission-daemon-config-dir "/watch"))
+(define %transmission-daemon-incomplete-dir
+  (string-append %transmission-daemon-config-dir "/incomplete"))
+
+(define %transmission-daemon-settings-file
+  (string-append %transmission-daemon-config-dir "/settings.json"))
+
+(define %transmission-daemon-peer-port 51000) ; default is 51413
+
+(define %transmission-daemon-rpc-port 9999)   ; default is 9091
+(define %transmission-daemon-rpc-username "test-username")
+(define %transmission-daemon-rpc-password "test-password")
+
+(define %transmission-daemon-test-configuration
+  (transmission-daemon-configuration
+   (incomplete-dir-enabled? #t)
+   (incomplete-dir %transmission-daemon-incomplete-dir)
+
+   (watch-dir-enabled? #t)
+   (watch-dir %transmission-daemon-watch-dir)
+
+   (peer-port-random-on-start? #f)
+   (peer-port %transmission-daemon-peer-port)
+
+   (rpc-enabled? #t)
+   (rpc-port %transmission-daemon-rpc-port)
+   (rpc-whitelist-enabled? #f)
+   (rpc-authentication-required? #t)
+   (rpc-username %transmission-daemon-rpc-username)
+   (rpc-password (transmission-password-hash %transmission-daemon-rpc-password
+                                             "yEK0q3.X"))))
+
+(define (run-transmission-daemon-test)
+  (define os
+    (marionette-operating-system
+     (simple-operating-system
+      (service dhcp-client-service-type)
+      (service transmission-daemon-service-type
+               %transmission-daemon-test-configuration))
+     #:imported-modules '((gnu services herd)
+                          (json parser))
+     #:requirements '(transmission-daemon)))
+
+  (define test
+    (with-imported-modules '((gnu build marionette))
+      #~(begin
+          (use-modules (gnu build marionette)
+                       (srfi srfi-64))
+
+          (define marionette
+            (make-marionette
+             (list #$(virtual-machine
+                      (operating-system os)
+                      (port-forwardings
+                       `((9091 . ,%transmission-daemon-rpc-port)))))))
+
+          (mkdir #$output)
+          (chdir #$output)
+
+          (test-begin "transmission-daemon")
+
+          ;; Make sure the "transmission" user and group have been created.
+          (test-assert "\"transmission\" user exists"
+            (marionette-eval
+             '(begin
+                (getpwnam #$%transmission-daemon-user)
+                #t)
+             marionette))
+          (test-assert "\"transmission\" group exists"
+            (marionette-eval
+             '(begin
+                (getgrnam #$%transmission-daemon-group)
+                #t)
+             marionette))
+
+          ;; Make sure Transmission Daemon's configuration directory has been
+          ;; created with the correct ownership and permissions.
+          (test-assert "configuration directory exists"
+            (marionette-eval
+             '(eq? (stat:type (stat #$%transmission-daemon-config-dir))
+                   'directory)
+             marionette))
+          (test-assert "configuration directory has correct ownership"
+            (marionette-eval
+             '(let ((config-dir (stat #$%transmission-daemon-config-dir))
+                    (transmission-user (getpwnam #$%transmission-daemon-user)))
+                (and (eqv? (stat:uid config-dir)
+                           (passwd:uid transmission-user))
+                     (eqv? (stat:gid config-dir)
+                           (passwd:gid transmission-user))))
+             marionette))
+          (test-assert "configuration directory has expected permissions"
+            (marionette-eval
+             '(eqv? (stat:perms (stat #$%transmission-daemon-config-dir))
+                    #o750)
+             marionette))
+
+          ;; Make sure the incomplete-downloads and watch directories have been
+          ;; created with the correct ownership and permissions.
+          (test-assert "incomplete-downloads directory exists"
+            (marionette-eval
+             '(eq? (stat:type (stat #$%transmission-daemon-incomplete-dir))
+                   'directory)
+             marionette))
+          (test-assert "incomplete-downloads directory has correct ownership"
+            (marionette-eval
+             '(let ((incomplete-dir
+                     (stat #$%transmission-daemon-incomplete-dir))
+                    (transmission-user
+                     (getpwnam #$%transmission-daemon-user)))
+                (and (eqv? (stat:uid incomplete-dir)
+                           (passwd:uid transmission-user))
+                     (eqv? (stat:gid incomplete-dir)
+                           (passwd:gid transmission-user))))
+             marionette))
+          (test-assert
+              "incomplete-downloads directory has expected permissions"
+            (marionette-eval
+             '(eqv? (stat:perms (stat #$%transmission-daemon-incomplete-dir))
+                    #o750)
+             marionette))
+
+          (test-assert "watch directory exists"
+            (marionette-eval
+             '(eq? (stat:type (stat #$%transmission-daemon-watch-dir))
+                   'directory)
+             marionette))
+          (test-assert "watch directory has correct ownership"
+            (marionette-eval
+             '(let ((watch-dir (stat #$%transmission-daemon-watch-dir))
+                    (transmission-user (getpwnam #$%transmission-daemon-user)))
+                (and (eqv? (stat:uid watch-dir)
+                           (passwd:uid transmission-user))
+                     (eqv? (stat:gid watch-dir)
+                           (passwd:gid transmission-user))))
+             marionette))
+          (test-assert "watch directory has expected permissions"
+            (marionette-eval
+             '(eqv? (stat:perms (stat #$%transmission-daemon-watch-dir))
+                    #o770)
+             marionette))
+
+          ;; Make sure the settings file has been created and appears valid.
+          (test-assert "settings file exists"
+            (marionette-eval
+             '(file-exists? #$%transmission-daemon-settings-file)
+             marionette))
+          (test-assert "settings file is valid JSON"
+            (marionette-eval
+             '(begin
+                (use-modules (json parser))
+                (with-input-from-file #$%transmission-daemon-settings-file
+                  (lambda ()
+                    (json->scm)))
+                #t)
+             marionette))
+          (test-assert "settings file contains a non-empty JSON object"
+            (marionette-eval
+             '(begin
+                (use-modules (json parser)
+                             (srfi srfi-1))
+                (let ((settings (with-input-from-file
+                                    #$%transmission-daemon-settings-file
+                                  (lambda ()
+                                    (json->scm)))))
+                  (and (list? settings)
+                       (not (null? settings))
+                       (every pair? settings))))
+             marionette))
+
+          ;; Make sure Transmission Daemon is running.
+          (test-assert "transmission-daemon is running"
+            (marionette-eval
+             '(begin
+                (use-modules (gnu services herd))
+                (live-service-running
+                 (find (lambda (live-service)
+                         (memq 'transmission-daemon
+                               (live-service-provision live-service)))
+                       (current-services))))
+             marionette))
+
+          ;; Make sure the daemon is listening for peer connections.
+          (test-assert "transmission-daemon is listening for peers"
+            (wait-for-tcp-port #$%transmission-daemon-peer-port marionette))
+
+          ;; Make sure the daemon is listening for RPC-client connections.
+          (test-assert "transmission-daemon is listening for RPC clients"
+            (wait-for-tcp-port #$%transmission-daemon-rpc-port marionette))
+
+          ;; Make sure the RPC-authentication settings are honored.
+          (test-assert "transmission-daemon requires RPC authentication"
+            (let ((transmission-remote
+                   (string-append #+transmission "/bin/transmission-remote")))
+              (with-error-to-port (%make-void-port "w")
+                (lambda ()
+                  (not (zero? (system* transmission-remote
+                                       "--session-info")))))))
+          (test-assert "transmission-daemon rejects incorrect RPC credentials"
+            (let ((transmission-remote
+                   (string-append #+transmission "/bin/transmission-remote"))
+                  (wrong-auth-string
+                   (string-append #$%transmission-daemon-rpc-username
+                                  ":"
+                                  "wrong-"
+                                  #$%transmission-daemon-rpc-password)))
+              (with-error-to-port (%make-void-port "w")
+                (lambda ()
+                  (not (zero? (system* transmission-remote
+                                       "--auth" wrong-auth-string
+                                       "--session-info")))))))
+          (test-assert "transmission-daemon accepts correct RPC credentials"
+            (let ((transmission-remote
+                   (string-append #+transmission "/bin/transmission-remote"))
+                  (auth-string
+                   (string-append #$%transmission-daemon-rpc-username
+                                  ":"
+                                  #$%transmission-daemon-rpc-password)))
+              (with-output-to-port (%make-void-port "w")
+                (lambda ()
+                  (zero? (system* transmission-remote
+                                  "--auth" auth-string
+                                  "--session-info"))))))
+
+          (test-end)
+          (exit (= (test-runner-fail-count (test-runner-current)) 0)))))
+
+  (gexp->derivation "transmission-daemon-test" test))
+
+(define %test-transmission-daemon
+  (system-test
+   (name "transmission-daemon")
+   (description "Test a running Transmission Daemon service.")
+   (value (run-transmission-daemon-test))))