Testing of static front-end resource customization

One important missing test is that the content of the customized
resource is read from storage every time rather than once. Testing
that requirement would involve creating temporary files which is a
little more work.

test/meson.build

@@ -36,7 +36,10 @@ if gtest_dep.found() and not meson.is_cross_build()
       'zimfile&other.zim',
       'corner_cases.zim',
       'poor.zim',
-      'library.xml'
+      'library.xml',
+      'customized_resources.txt',
+      'helloworld.txt',
+      'welcome.html',
     ]
     foreach file : data_files
         # configure_file(input : 'data/' + file,