Add test that confirms behavior when PATH is unset

- Path will likely contain more results from using `confstr`, this checks only
    the default

tests/checks/broken-config.fish

@@ -22,3 +22,9 @@ end
 # should not crash or segfault in the presence of an invalid locale
 LC_ALL=hello echo hello world
 # CHECK: hello world
+
+# FIXME: Rationalize behavior when PATH is explicitly unset, should this not behave like PATH=""?
+# "" is threated like ".", see https://github.com/fish-shell/fish-shell/issues/3914
+env -u PATH $fish --no-config -c 'contains -- /usr/bin $PATH; and contains -- /bin $PATH'
+and echo PATH has something when unset
+# CHECK: PATH has something when unset