diff --git a/maths/3n+1.py b/maths/3n+1.py
index 6b2dfc785794..ff769550297c 100644
--- a/maths/3n+1.py
+++ b/maths/3n+1.py
@@ -23,15 +23,16 @@ def n31(a: int) -> Tuple[List[int], int]:
     return path, len(path)
 
 
-def main():
-    num = 4
-    path, length = n31(num)
-    print(
-        "The Collatz sequence of {0} took {1} steps. \nPath: {2}".format(
-            num, length, path
-        )
-    )
+def test_n31():
+    """
+    >>> test_n31()
+    """
+    assert n31(4) == ([4, 2, 1], 3)
+    assert n31(11) == ([11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1], 15)
+    assert n31(31) == ([31, 94, 47, 142, 71, 214, 107, 322, 161, 484, 242, 121, 364, 182, 91, 274, 137, 412, 206, 103, 310, 155, 466, 233, 700, 350, 175, 526, 263, 790, 395, 1186, 593, 1780, 890, 445, 1336, 668, 334, 167, 502, 251, 754, 377, 1132, 566, 283, 850, 425, 1276, 638, 319, 958, 479, 1438, 719, 2158, 1079, 3238, 1619, 4858, 2429, 7288, 3644, 1822, 911, 2734, 1367, 4102, 2051, 6154, 3077, 9232, 4616, 2308, 1154, 577, 1732, 866, 433, 1300, 650, 325, 976, 488, 244, 122, 61, 184, 92, 46, 23, 70, 35, 106, 53, 160, 80, 40, 20, 10, 5, 16, 8, 4, 2, 1], 107)
 
 
 if __name__ == "__main__":
-    main()
+    num = 4
+    path, length = n31(num)
+    print(f"The Collatz sequence of {num} took {length} steps. \nPath: {path}")
diff --git a/maths/abs.py b/maths/abs.py
index 7509c5c20a22..68c99a1d51d8 100644
--- a/maths/abs.py
+++ b/maths/abs.py
@@ -5,18 +5,24 @@ def abs_val(num):
     """
     Find the absolute value of a number.
 
-    >>abs_val(-5)
-    5
-    >>abs_val(0)
+    >>> abs_val(-5.1)
+    5.1
+    >>> abs_val(-5) == abs_val(5)
+    True
+    >>> abs_val(0)
     0
     """
     return -num if num < 0 else num
 
 
-def main():
-    """Print absolute value of -34."""
-    print(abs_val(-34))  # = 34
+def test_abs_val():
+    """
+    >>> test_abs_val()
+    """
+    assert 0 == abs_val(0)
+    assert 34 == abs_val(34)
+    assert 100000000000 == abs_val(-100000000000)
 
 
 if __name__ == "__main__":
-    main()
+    print(abs_val(-34))  # --> 34
diff --git a/maths/average_mean.py b/maths/average_mean.py
index 77464ef5d9f7..4beca1f741a0 100644
--- a/maths/average_mean.py
+++ b/maths/average_mean.py
@@ -3,14 +3,18 @@
 
 def average(nums):
     """Find mean of a list of numbers."""
-    avg = sum(nums) / len(nums)
-    return avg
+    return sum(nums) / len(nums)
 
 
-def main():
-    """Call average module to find mean of a specific list of numbers."""
-    print(average([2, 4, 6, 8, 20, 50, 70]))
+def test_average():
+    """
+    >>> test_average()
+    """
+    assert 12.0 == average([3, 6, 9, 12, 15, 18, 21])
+    assert 20 == average([5, 10, 15, 20, 25, 30, 35])
+    assert 4.5 == average([1, 2, 3, 4, 5, 6, 7, 8])
 
 
 if __name__ == "__main__":
-    main()
+    """Call average module to find mean of a specific list of numbers."""
+    print(average([2, 4, 6, 8, 20, 50, 70]))