diff --git a/illustrations/1_tester/test_unitaire.py b/illustrations/1_tester/test_unitaire.py
index 3a0ff33..4cba9b5 100644
--- a/illustrations/1_tester/test_unitaire.py
+++ b/illustrations/1_tester/test_unitaire.py
@@ -5,11 +5,22 @@ def est_premier(n):
     >>> est_premier(5)
     True
     >>> est_premier(4)
-    True
+    False
     """
-    for k in range(n):
-        if k % n == 0:
+    for k in range(2, n):
+        if n % k == 0:
             return False
 
     return True
 
+# Exercice: Soit S un string
+# S = mot_1 mot_2 … mot_n
+# renvoyez miroir(mot_1) … miroir(mot_n)
+def reverse_words(S):
+    """
+    >>> reverse_words("abc def")
+    cba fed
+    >>> reverse_words("bonjour bonsoir")
+    roujnob riosnob
+    """
+    pass