diff --git a/Library/Homebrew/test/lib/config.rb b/Library/Homebrew/test/lib/config.rb
index 10c3c8cd75..91ef9fe8af 100644
--- a/Library/Homebrew/test/lib/config.rb
+++ b/Library/Homebrew/test/lib/config.rb
@@ -10,12 +10,15 @@ TEST_TMPDIR = ENV.fetch("HOMEBREW_TEST_TMPDIR") { |k|
   ENV[k] = dir
 }
 
-HOMEBREW_PREFIX        = Pathname.new(TEST_TMPDIR).join("prefix")
-HOMEBREW_REPOSITORY    = HOMEBREW_PREFIX
-HOMEBREW_LIBRARY       = HOMEBREW_REPOSITORY+"Library"
+# Paths pointing into the Homebrew code base that persist across test runs
 HOMEBREW_LIBRARY_PATH  = Pathname.new(File.expand_path("../../..", __FILE__))
 HOMEBREW_ENV_PATH      = HOMEBREW_LIBRARY_PATH.parent+"ENV"
 HOMEBREW_LOAD_PATH     = [File.expand_path("..", __FILE__), HOMEBREW_LIBRARY_PATH].join(":")
+
+# Paths redirected to a temporary directory and wiped at the end of the test run
+HOMEBREW_PREFIX        = Pathname.new(TEST_TMPDIR).join("prefix")
+HOMEBREW_REPOSITORY    = HOMEBREW_PREFIX
+HOMEBREW_LIBRARY       = HOMEBREW_REPOSITORY+"Library"
 HOMEBREW_CACHE         = HOMEBREW_PREFIX.parent+"cache"
 HOMEBREW_CACHE_FORMULA = HOMEBREW_PREFIX.parent+"formula_cache"
 HOMEBREW_LOCK_DIR      = HOMEBREW_PREFIX.parent+"locks"