diff --git a/pyCatSim/api/cat.py b/pyCatSim/api/cat.py
index 404044a..7e78664 100644
--- a/pyCatSim/api/cat.py
+++ b/pyCatSim/api/cat.py
@@ -329,7 +329,7 @@ def eat(self):
         return {"hunger_level": self.hunger_level, "mood": self.mood}
 
 
-    def sleep(self, duration=0):
+    def sleep(self, duration):
         """
         Simulates the cat getting some sleep.
 
@@ -340,7 +340,7 @@ def sleep(self, duration=0):
 
         Parameters
         ----------
-        duration : int or float, optional
+        duration : int or float
             Number of hours the cat sleeps. Must be an integer or float. The default is 0.
 
         Raises
diff --git a/pyCatSim/tests/test_api_Cat.py b/pyCatSim/tests/test_api_Cat.py
index a5b949e..f5d8d3b 100644
--- a/pyCatSim/tests/test_api_Cat.py
+++ b/pyCatSim/tests/test_api_Cat.py
@@ -162,19 +162,21 @@ class TestcatCatSleep:
                              [
                                  (0),
                                  (1),
-                                 (4.4),
+                                 (14.4),
                                  pytest.param("kitty", marks=pytest.mark.xfail),
                                  pytest.param(-1, marks=pytest.mark.xfail),
                                  pytest.param(17, marks=pytest.mark.xfail)
                                  ]
                              )
     def test_sleep_t0(self, duration):
-        cat = Cat(name="Boots", color="tabby")
+        cat = Cat(name="Boots", color="tabby", energy=0)
 
         cat.sleep(duration)
         
         if duration < 3:
             assert cat.energy == 0
+	if ((duration >= 12) and (duration < 15)):
+	    assert cat.energy == 4
 
 
 class TestcatCatFact:
@@ -197,4 +199,4 @@ def test_give_fact_t0(self):
         "Cats use their whiskers to detect changes in their surroundings.",
         "The average house cat can run at speeds up to 30 mph.",
         "Cats meow only to communicate with humans."
-    ]
\ No newline at end of file
+    ]