diff --git a/python/16_bsearch/bsearch_variants.py b/python/16_bsearch/bsearch_variants.py
index 0b699556..a482fce8 100644
--- a/python/16_bsearch/bsearch_variants.py
+++ b/python/16_bsearch/bsearch_variants.py
@@ -5,6 +5,7 @@
 
 from typing import List
 
+
 def bsearch_left(nums: List[int], target: int) -> int:
     """Binary search of the index of the first element
     equal to a given target in the ascending sorted array.
@@ -58,6 +59,7 @@ def bsearch_left_not_less(nums: List[int], target: int) -> int:
     else:
         return -1
 
+
 def bsearch_right_not_greater(nums: List[int], target: int) -> int:
     """Binary search of the index of the last element
     not greater than a given target in the ascending sorted array.
@@ -75,6 +77,24 @@ def bsearch_right_not_greater(nums: List[int], target: int) -> int:
     else:
         return -1
 
+
+def test_bsearch_left_not_less():
+    a = bsearch_left_not_less([1, 2, 5], 1)
+    assert a == 0
+    a = bsearch_left_not_less([1, 2, 5], 5)
+    assert a == 2
+    a = bsearch_left_not_less([1, 2, 5], 2)
+    assert a == 1
+    a = bsearch_left_not_less([1, 2, 3, 3, 5], 2)
+    assert a == 1
+    a = bsearch_left_not_less([1, 2, 3, 3, 5], 6)
+    assert a == -1
+    a = bsearch_left_not_less([], 1)
+    assert a == -1
+    a = bsearch_left_not_less([1], 1)
+    assert a == 0
+
+
 if __name__ == "__main__":
     a = [1, 1, 2, 3, 4, 6, 7, 7, 7, 7, 10, 22]
 
@@ -86,9 +106,7 @@ def bsearch_right_not_greater(nums: List[int], target: int) -> int:
     print(bsearch_right(a, 7) == 9)
     print(bsearch_right(a, 30) == -1)
 
-    print(bsearch_left_not_less(a, 0) == 0)
-    print(bsearch_left_not_less(a, 5) == 5)
-    print(bsearch_left_not_less(a, 30) == -1)
+    test_bsearch_left_not_less()
 
     print(bsearch_right_not_greater(a, 0) == -1)
     print(bsearch_right_not_greater(a, 6) == 5)