Does it need to be a tuple for the tests to succeed?

easybuild/tools/config.py

@@ -120,7 +120,7 @@
 DEFAULT_PR_TARGET_ACCOUNT = 'easybuilders'
 DEFAULT_PREFIX = os.path.join(os.path.expanduser('~'), ".local", "easybuild")
 DEFAULT_REPOSITORY = 'FileRepository'
-DEFAULT_EXTRA_SOURCE_URLS = ['https://sources.easybuild.io/']
+DEFAULT_EXTRA_SOURCE_URLS = ('https://sources.easybuild.io/',)
 # Filter these CUDA libraries by default from the RPATH sanity check.
 # These are the only four libraries for which the CUDA toolkit ships stubs. By design, one is supposed to build
 # against the stub versions, but use the libraries that come with the CUDA driver at runtime. That means they should

easybuild/tools/options.py

@@ -410,7 +410,7 @@ def override_options(self):
             'extra-modules': ("List of extra modules to load after setting up the build environment",
                               'strlist', 'extend', None),
             "extra-source-urls": ("Specify URLs to fetch sources from in addition to those in the easyconfig",
-                                  "urllist", "add_flex", DEFAULT_EXTRA_SOURCE_URLS, {'metavar': 'URL[%sURL]' % '|'}),
+                                  "urltuple", "add_flex", DEFAULT_EXTRA_SOURCE_URLS, {'metavar': 'URL[%sURL]' % '|'}),
             'fetch': ("Allow downloading sources ignoring OS and modules tool dependencies, "
                       "implies --stop=fetch, --ignore-osdeps and ignore modules tool", None, 'store_true', False),
             'filter-deps': ("List of dependencies that you do *not* want to install with EasyBuild, "