syncthing: fix badly escaped ignore patterns test

The previous test would pass no matter what the `ignoreString` was. I
don't know enough Bash/Grep to explain it, but it was easy to test by
just changing the pattern to have `WRONG` instead of `val1`, and that
would still pass the `assertFileContains` test.

I've hopefully fixed it now, by using `lib.escapeShellArg` before
passing it to `assertFileContains`, and I've also added a negative test
case, to ensure that a bad ignore string is _not_ found in the merge
script.

tests/modules/services/syncthing/linux/ignore-patterns.nix

@@ -1,3 +1,5 @@
+{ lib, ... }:
+
 {
   services.syncthing = {
     enable = true;
@@ -19,9 +21,8 @@
 
   nmt.script =
     let
-      ignoreString = ''
-        {"ignore":["val1","!val2","*al3","val'\'''4","val\"5"]}
-      '';
+      ignoreString = ''{"ignore":["val1","!val2","*al3","val'\'''4","val\"5"]}'';
+      ignoreStringBad = ''{"ignore":["WRONG","!val2","*al3","val'\'''4","val\"5"]}'';
     in
     ''
       serviceFile=home-files/.config/systemd/user/syncthing-init.service
@@ -30,7 +31,10 @@
       assertFileContains "$serviceFile" "ExecStart="
 
       updateScript=$(grep -o '/nix/store/[^ ]*-merge-syncthing-config' "$TESTED/$serviceFile")
-      assertFileContains "$updateScript" '${ignoreString}'
       assertFileContains "$updateScript" "/rest/db/ignores?folder=ew8bc-4uanl"
+      assertFileContains "$updateScript" ${lib.escapeShellArg ignoreString}
+      if grep -qF ${lib.escapeShellArg ignoreStringBad} "$(_abs "$updateScript")"; then
+        fail "syncthing bad ignore string shouldn't be found in updateScript"
+      fi
     '';
 }