Add test and comment for `PATH#existing`.

1 files changed, 4 insertions, 0 deletions

diff --git a/Library/Homebrew/test/PATH_spec.rb b/Library/Homebrew/test/PATH_spec.rb
index b20a3d3ac..68233c23c 100644
--- a/Library/Homebrew/test/PATH_spec.rb
+++ b/Library/Homebrew/test/PATH_spec.rb
@@ -107,5 +107,9 @@ describe PATH do
       expect(path.existing.to_ary).to eq(["/path1"])
       expect(path.to_ary).to eq(["/path1", "/path2"])
     end
+
+    it "returns nil instead of an empty #{described_class}" do
+      expect(described_class.new.existing).to be nil
+    end
   end
 end