diff --git a/cmd/test-bot.rb b/cmd/test-bot.rb
index 67e30e6d..99812a41 100755
--- a/cmd/test-bot.rb
+++ b/cmd/test-bot.rb
@@ -43,6 +43,8 @@ def test_bot_args
                           "passing output as raw bytes instead of re-encoding in UTF-8."
       switch "--test-default-formula",
              description: "Use a default testing formula when not building a tap and no other formulae are specified."
+      switch "--test-default-cask",
+             description: "Use a default testing cask when not building a tap and no other formulae are specified."
       flag   "--root-url=",
              description: "Use the specified <URL> as the root of the bottle's URL instead of Homebrew's default."
       flag   "--git-name=",
diff --git a/lib/test_runner.rb b/lib/test_runner.rb
index c4fa84a8..5c7e1d50 100644
--- a/lib/test_runner.rb
+++ b/lib/test_runner.rb
@@ -142,14 +142,14 @@ def build_tests(argument, tap:, git:, output_paths:, skip_setup:,
                           args.deleted_formulae.nil?
       if no_formulae_flags &&
          (no_only_args || args.only_formulae? || args.only_formulae_detect?)
-        tests[:formulae_detect] = Tests::PackagesDetect.new(argument, tap:       tap,
-                                                                      git:       git,
+        tests[:formulae_detect] = Tests::PackagesDetect.new(argument, tap:,
+                                                                      git:,
                                                                       dry_run:   args.dry_run?,
                                                                       fail_fast: args.fail_fast?,
                                                                       verbose:   args.verbose?)
-      elsif (no_only_args || args.only_casks_detect?)
-        tests[:casks_detect] = Tests::PackagesDetect.new(argument, tap:       tap,
-                                                                   git:       git,
+      elsif no_only_args || args.only_casks_detect?
+        tests[:casks_detect] = Tests::PackagesDetect.new(argument, tap:,
+                                                                   git:,
                                                                    dry_run:   args.dry_run?,
                                                                    fail_fast: args.fail_fast?,
                                                                    verbose:   args.verbose?)
diff --git a/lib/tests/packages_detect.rb b/lib/tests/packages_detect.rb
index 8ae8053c..971e071b 100644
--- a/lib/tests/packages_detect.rb
+++ b/lib/tests/packages_detect.rb
@@ -3,7 +3,7 @@
 module Homebrew
   module Tests
     class PackagesDetect < Test
-      attr_reader :testing_formulae, :added_formulae, :deleted_formulae, 
+      attr_reader :testing_formulae, :added_formulae, :deleted_formulae,
                   :testing_casks, :added_casks, :deleted_casks
 
       def initialize(argument, tap:, git:, dry_run:, fail_fast:, verbose:)
@@ -60,6 +60,7 @@ def detect_packages!(args:)
           end
 
           @testing_formulae = [canonical_formula_name]
+          @testing_casks = []
         else
           raise UsageError,
                 "#{@argument} is not detected from GitHub Actions or a formula name!"
@@ -139,20 +140,14 @@ def detect_packages!(args:)
 
         if tap && diff_start_sha1 != diff_end_sha1
           formula_path = tap.formula_dir.to_s
-          @added_formulae +=
-            diff_packages(diff_start_sha1, diff_end_sha1, formula_path, "A")
-          modified_formulae +=
-            diff_packages(diff_start_sha1, diff_end_sha1, formula_path, "M")
-          @deleted_formulae +=
-            diff_packages(diff_start_sha1, diff_end_sha1, formula_path, "D")
+          @added_formulae += diff_packages(diff_start_sha1, diff_end_sha1, formula_path, "A")
+          modified_formulae += diff_packages(diff_start_sha1, diff_end_sha1, formula_path, "M")
+          @deleted_formulae += diff_packages(diff_start_sha1, diff_end_sha1, formula_path, "D")
 
           cask_path = tap.cask_dir.to_s
-          @added_casks += @added_formulae +
-                             diff_packages(diff_start_sha1, diff_end_sha1, cask_path, "A")
-          modified_casks += modified_formulae +
-                               diff_packages(diff_start_sha1, diff_end_sha1, cask_path, "M")
-          @deleted_casks += @deleted_formulae +
-                               diff_packages(diff_start_sha1, diff_end_sha1, cask_path, "D")
+          @added_casks += diff_packages(diff_start_sha1, diff_end_sha1, cask_path, "A")
+          modified_casks += diff_packages(diff_start_sha1, diff_end_sha1, cask_path, "M")
+          @deleted_casks += diff_packages(diff_start_sha1, diff_end_sha1, cask_path, "D")
         end
 
         # If a package is both added and deleted: it's actually modified.
@@ -169,8 +164,8 @@ def detect_packages!(args:)
         if args.test_default_formula?
           # Build the default test formula.
           modified_formulae << "homebrew/test-bot/testbottest"
-          modified_casks << "homebrew/test-bot/testbottest"
         end
+        modified_casks << "homebrew/test-bot/testbottest" if args.test_default_cask?
 
         @testing_formulae += @added_formulae + modified_formulae
         @testing_casks += @added_casks + modified_casks
@@ -189,6 +184,7 @@ def detect_packages!(args:)
         @added_formulae.uniq!
         modified_formulae.uniq!
         @deleted_formulae.uniq!
+
         @testing_casks.uniq!
         @added_casks.uniq!
         modified_casks.uniq!
@@ -264,14 +260,11 @@ def diff_packages(start_revision, end_revision, path, filter)
         ).lines.filter_map do |line|
           file = Pathname.new line.chomp
 
-          name = nil
           if tap.formula_file?(file)
-            name = tap.formula_file_to_name(file)
+            tap.formula_file_to_name(file)
           elsif tap.cask_file?(file)
-            name = file.basename(".rb").to_s
+            file.basename(".rb").to_s
           end
-
-          name
         end.compact
       end
     end