tests: fix test.assert.assertions.enable not working

Co-authored-by: Robert Helgesson <robert@rycee.net>

tests/asserts.nix

@@ -37,17 +37,13 @@ with lib;
     };
   };
 
-  config = mkIf config.test.asserts.warnings.enable {
+  config = mkMerge [
+    (mkIf config.test.asserts.warnings.enable {
       home.file = {
         "asserts/warnings.actual".text = concatStringsSep ''
 
           --
         '' config.warnings;
-
-      "asserts/assertions.actual".text = concatStringsSep ''
-
-        --
-      '' (map (x: x.message) (filter (x: !x.assertion) config.assertions));
       };
 
       nmt.script = ''
@@ -59,7 +55,18 @@ with lib;
               --
             '' config.test.asserts.warnings.expected)
           }
+      '';
+    })
 
+    (mkIf config.test.asserts.assertions.enable {
+      home.file = {
+        "asserts/assertions.actual".text = concatStringsSep ''
+
+          --
+        '' (map (x: x.message) (filter (x: !x.assertion) config.assertions));
+      };
+
+      nmt.script = ''
         assertFileContent \
           home-files/asserts/assertions.actual \
           ${
@@ -69,5 +76,6 @@ with lib;
             '' config.test.asserts.assertions.expected)
           }
       '';
-  };
+    })
+  ];
 }