add test for brew cask --cache

Library/Homebrew/test/cask/cmd/--cache_spec.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+require_relative "shared_examples/requires_cask_token"
+require_relative "shared_examples/invalid_option"
+
+describe Cask::Cmd::Cache, :cask do
+  let(:local_transmission) {
+    Cask::CaskLoader.load(cask_path("local-transmission"))
+  }
+
+  let(:local_caffeine) {
+    Cask::CaskLoader.load(cask_path("local-caffeine"))
+  }
+
+  it_behaves_like "a command that requires a Cask token"
+  it_behaves_like "a command that handles invalid options"
+
+  it "prints the file used to cache the Cask" do
+    transmission_location = CurlDownloadStrategy.new(
+      local_transmission.url.to_s, local_transmission.token, local_transmission.version,
+      cache: Cask::Cache.path, **local_transmission.url.specs
+    ).cached_location
+    caffeine_location = CurlDownloadStrategy.new(
+      local_caffeine.url.to_s, local_caffeine.token, local_caffeine.version,
+      cache: Cask::Cache.path, **local_caffeine.url.specs
+    ).cached_location
+
+    expect do
+      described_class.run("local-transmission", "local-caffeine")
+    end.to output("#{transmission_location}\n#{caffeine_location}\n").to_stdout
+  end
+
+  it "properly handles Casks that are not present" do
+    expect {
+      described_class.run("notacask")
+    }.to raise_error(Cask::CaskUnavailableError)
+  end
+end