Protect against rolling back to a bad version

test/cli/main_test.rb

@@ -5,4 +5,18 @@ class CliMainTest < CliTestCase
     version = stdouted { Mrsk::Cli::Main.new.version }
     assert_equal Mrsk::VERSION, version
   end
+
+  test "rollback bad version" do
+    run_command("details") # Preheat MRSK const
+
+    run_command("rollback", "nonsense").tap do |output|
+      assert_match /docker container ls -a --filter label=service=app --format '{{ .Names }}'/, output
+      assert_match /The app version 'nonsense' is not available as a container/, output
+    end
+  end
+
+  private
+    def run_command(*command)
+      stdouted { Mrsk::Cli::Main.start([*command, "-c", "test/fixtures/deploy_with_accessories.yml"]) }
+    end
 end