[bug#28600] [PATCH] tests: install: Switch to modifying the gc-root-service-type.

[Christopher Baines]

Rather than adding the service to the system.

The previous approach is causing the system tests to fail, as the os already
contains a service of type gc-root-service-type, and the way that this service
extends the system-service doesn't compose, causing an error if its added
twice.

  ERROR: In procedure symlink: File exists

* gnu/tests/install.scm (operating-system-with-gc-roots): Modify the existing
  gc-root-service, rather than adding another.
---
 gnu/tests/install.scm | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/gnu/tests/install.scm b/gnu/tests/install.scm
index 49743860e..28dfc3b8b 100644
--- a/gnu/tests/install.scm
+++ b/gnu/tests/install.scm
@@ -127,8 +127,9 @@
   "Return a variant of OS where ROOTS are registered as GC roots."
   (operating-system
     (inherit os)
-    (services (cons (service gc-root-service-type roots)
-                    (operating-system-user-services os)))))
+    (services
+     (modify-services (operating-system-user-services os)
+       (gc-root-service-type _ => roots)))))
 
 
 (define MiB (expt 2 20))
-- 
2.14.1