diff --git a/Monadoro.cabal b/Monadoro.cabal
--- a/Monadoro.cabal
+++ b/Monadoro.cabal
@@ -1,17 +1,17 @@
 cabal-version: 1.12
 
--- This file has been generated from package.yaml by hpack version 0.34.4.
+-- This file has been generated from package.yaml by hpack version 0.35.0.
 --
 -- see: https://github.com/sol/hpack
 
 name:           Monadoro
-version:        0.3.6.2
+version:        0.4.0.0
 synopsis:       A minimalistic CLI Pomodoro timer.
 description:    A Pomodoro timer with two modes: single-pomodoro (default), and four-pomodoro (`--session`).
 category:       Tools
 author:         Patryk Kocielnik
 maintainer:     patryk@kocielnik.pl
-copyright:      2018-2022 Patryk Kocielnik
+copyright:      2018-2025 Patryk Kocielnik
 license:        MIT
 license-file:   LICENSE
 build-type:     Simple
@@ -47,7 +47,6 @@
       Paths_Monadoro
   hs-source-dirs:
       app
-  ghc-options: -threaded -rtsopts -with-rtsopts=-N
   build-depends:
       Monadoro
     , base >=4.7 && <5
@@ -62,12 +61,10 @@
       Paths_Monadoro
   hs-source-dirs:
       test
-  ghc-options: -threaded -rtsopts -with-rtsopts=-N
   build-depends:
       Monadoro
     , base >=4.7 && <5
     , doctest >=0.8
-    , hspec
     , process >=1.6 && <2
     , time >=1.8 && <2
   default-language: Haskell2010
diff --git a/changelog b/changelog
--- a/changelog
+++ b/changelog
@@ -1,3 +1,16 @@
+monadoro (4.0.0)
+
+	* Add a newline in the end of timer countdown.
+
+	Each countdown was missing a newline character when it ended.
+
+	MacOS showed this explicitly, with a percent mark (`%`), after each
+	such line. Thanks to that I found this problem.
+
+	The test is not coupled to this behavior. I have not found a way to
+	test this with DocTest, and without DocTest the test would not have
+	been as clear.
+
 monadoro (3.6.2)
 
 	* Test an internal method for printing usage.
diff --git a/src/CLI.hs b/src/CLI.hs
--- a/src/CLI.hs
+++ b/src/CLI.hs
@@ -58,9 +58,14 @@
 runSession :: [String] -> IO ()
 runSession xs = session (getDelayIfNeeded xs)
 
+{-| runTimer
+
+>>> runTimer noDelay ["00:01"]
+...00:00
+-}
 runTimer :: IO () -> [String] -> IO ()
 runTimer delayer []     = void (countdownLoop delayer "25:00")
-runTimer delayer [t]    = void (countdownLoop delayer t)
+runTimer delayer [t]    = void (countdownLoop delayer t) >> putStrLn ""
 runTimer delayer (t:ts) = runTimer delayer [t] >> runTimer delayer ts
 
 filterParams :: [String] -> [String]
@@ -141,6 +146,9 @@
 getDelayIfNeeded xs
   | xs `containsEither` ["--nodelay", "-n"] = wait 0
   | otherwise = wait 1
+
+noDelay :: IO ()
+noDelay = wait 0
 
 milisecPerSecond :: Int
 milisecPerSecond = 10 ^ (6 :: Int)
diff --git a/src/ParseTime.lhs b/src/ParseTime.lhs
--- a/src/ParseTime.lhs
+++ b/src/ParseTime.lhs
@@ -99,6 +99,14 @@
 >
 > >>> count_down_time "01:00"
 > "00:59"
+>
+> What happens when an invalid period is given?
+>
+> >>> count_down_time "foo"
+> "*** Exception: Prelude.head: empty list
+>
+> Turns out Vim highlighting doesn't handle this lack
+> of double quotes well, but tests complete OK.
 > -}
 > 
 > count_down_time :: String -> String
diff --git a/test/Main.hs b/test/Main.hs
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -1,10 +1,36 @@
-import Test.DocTest
+import GHC.Stack.Types   (HasCallStack)
+import Test.DocTest      (doctest)
 
-main :: IO ()
-main = doctest [
+assert :: HasCallStack => Bool -> String
+assert False = error "Assertion failed!"
+assert _ = ""
+
+checkCondition :: HasCallStack => IO ()
+checkCondition
+  | result == "" = putStr ""
+  | otherwise = putStrLn result
+    where result = assert (0 /= 1)
+
+runOtherTests :: HasCallStack => IO ()
+runOtherTests = checkCondition
+
+runDocTests :: IO ()
+runDocTests = doctest [
         "-isrc",
         "src/CLI.hs",
         "src/ParseTime.lhs",
         "src/CountdownLoop.hs",
         "src/Pomodoro.lhs"
     ]
+
+main :: IO ()
+main = runDocTests >> runOtherTests
+
+-- These tests take 5 seconds to execute even when
+-- *nothing* was changed!
+--
+-- If something *was* changed, they take between *18
+-- and 26* seconds.
+--
+-- Pytest wouldn't take a *single second* to test all
+-- this! Can we get closer to that result?