diff --git a/searches/interpolation_search.py b/searches/interpolation_search.py
index db9893bdb..329596d34 100644
--- a/searches/interpolation_search.py
+++ b/searches/interpolation_search.py
@@ -11,9 +11,9 @@ except NameError:
 
 def interpolation_search(sorted_collection, item):
     """Pure implementation of interpolation search algorithm in Python
-    Be careful collection must be sorted, otherwise result will be
+    Be careful collection must be ascending sorted, otherwise result will be
     unpredictable
-    :param sorted_collection: some sorted collection with comparable items
+    :param sorted_collection: some ascending sorted collection with comparable items
     :param item: item value to search
     :return: index of found item or None if item is not found
     """
@@ -21,6 +21,13 @@ def interpolation_search(sorted_collection, item):
     right = len(sorted_collection) - 1
 
     while left <= right:
+        #avoid devided by 0 during interpolation
+        if sorted_collection[left]==sorted_collection[right]:
+            if sorted_collection[left]==item:
+                return left
+            else:
+                return None
+
         point = left + ((item - sorted_collection[left]) * (right - left)) // (sorted_collection[right] - sorted_collection[left])
         
         #out of range check
@@ -31,66 +38,97 @@ def interpolation_search(sorted_collection, item):
         if current_item == item:
             return point
         else:
-            if item < current_item:
-                right = point - 1
-            else:
-                left = point + 1
+            if point<left:
+                right = left
+                left = point
+            elif point>right:
+                left = right 
+                right = point
+            else:    
+                if item < current_item:
+                    right = point - 1
+                else:
+                    left = point + 1
     return None
 
-
 def interpolation_search_by_recursion(sorted_collection, item, left, right):
 
     """Pure implementation of interpolation search algorithm in Python by recursion
-    Be careful collection must be sorted, otherwise result will be
+    Be careful collection must be ascending sorted, otherwise result will be
     unpredictable
     First recursion should be started with left=0 and right=(len(sorted_collection)-1)
-    :param sorted_collection: some sorted collection with comparable items
+    :param sorted_collection: some ascending sorted collection with comparable items
     :param item: item value to search
     :return: index of found item or None if item is not found
     """
-    point = left + ((item - sorted_collection[left]) * (right - left)) // (sorted_collection[right] - sorted_collection[left])
 
+    #avoid devided by 0 during interpolation
+    if sorted_collection[left]==sorted_collection[right]:
+        if sorted_collection[left]==item:
+            return left
+        else:
+            return None
+
+    point = left + ((item - sorted_collection[left]) * (right - left)) // (sorted_collection[right] - sorted_collection[left])
+    
     #out of range check
     if point<0 or point>=len(sorted_collection):
         return None
 
     if sorted_collection[point] == item:
         return point
-    elif sorted_collection[point] > item:
-        return interpolation_search_by_recursion(sorted_collection, item, left, point-1)
+    elif point<left:
+        return interpolation_search_by_recursion(sorted_collection, item, point, left)
+    elif point>right:
+        return interpolation_search_by_recursion(sorted_collection, item, right, left)
     else:
-        return interpolation_search_by_recursion(sorted_collection, item, point+1, right)
+        if sorted_collection[point] > item:
+            return interpolation_search_by_recursion(sorted_collection, item, left, point-1)
+        else:
+            return interpolation_search_by_recursion(sorted_collection, item, point+1, right)
       
 def __assert_sorted(collection):
-    """Check if collection is sorted, if not - raises :py:class:`ValueError`
+    """Check if collection is ascending sorted, if not - raises :py:class:`ValueError`
     :param collection: collection
-    :return: True if collection is sorted
-    :raise: :py:class:`ValueError` if collection is not sorted
+    :return: True if collection is ascending sorted
+    :raise: :py:class:`ValueError` if collection is not ascending sorted
     Examples:
     >>> __assert_sorted([0, 1, 2, 4])
     True
     >>> __assert_sorted([10, -1, 5])
     Traceback (most recent call last):
     ...
-    ValueError: Collection must be sorted
+    ValueError: Collection must be ascending sorted
     """
     if collection != sorted(collection):
-        raise ValueError('Collection must be sorted')
+        raise ValueError('Collection must be ascending sorted')
     return True
 
 
 if __name__ == '__main__':
     import sys
-
-    user_input = raw_input('Enter numbers separated by comma:\n').strip()
+    
+    """
+	user_input = raw_input('Enter numbers separated by comma:\n').strip()
     collection = [int(item) for item in user_input.split(',')]
     try:
         __assert_sorted(collection)
     except ValueError:
-        sys.exit('Sequence must be sorted to apply interpolation search')
+        sys.exit('Sequence must be ascending sorted to apply interpolation search')
 
     target_input = raw_input('Enter a single number to be found in the list:\n')
     target = int(target_input)
+	"""
+
+    debug = 0
+    if debug == 1:
+        collection = [10,30,40,45,50,66,77,93]
+        try:
+            __assert_sorted(collection)
+        except ValueError:
+            sys.exit('Sequence must be ascending sorted to apply interpolation search')
+        target = 67
+        
     result = interpolation_search(collection, target)
     if result is not None:
         print('{} found at positions: {}'.format(target, result))
diff --git a/searches/quick_select.py b/searches/quick_select.py
index 1596cf040..76d09cb97 100644
--- a/searches/quick_select.py
+++ b/searches/quick_select.py
@@ -14,9 +14,9 @@ def _partition(data, pivot):
     """
     less, equal, greater = [], [], []
     for element in data:
-        if element.address < pivot.address:
+        if element < pivot:
             less.append(element)
-        elif element.address > pivot.address:
+        elif element > pivot:
             greater.append(element)
         else:
             equal.append(element)
@@ -24,6 +24,11 @@ def _partition(data, pivot):
     
 def quickSelect(list, k):
     #k = len(list) // 2 when trying to find the median (index that value would be when list is sorted)
+    
+    #invalid input
+    if k>=len(list) or k<0:
+        return None
+    
     smaller = []
     larger = []
     pivot = random.randint(0, len(list) - 1)
@@ -41,4 +46,4 @@ def quickSelect(list, k):
         return quickSelect(smaller, k)
     #must be in larger
     else:
-        return quickSelect(larger, k - (m + count))
+        return quickSelect(larger, k - (m + count))
\ No newline at end of file
diff --git a/searches/test_interpolation_search.py b/searches/test_interpolation_search.py
new file mode 100644
index 000000000..60bb3af22
--- /dev/null
+++ b/searches/test_interpolation_search.py
@@ -0,0 +1,93 @@
+import unittest
+from interpolation_search import interpolation_search, interpolation_search_by_recursion
+
+class Test_interpolation_search(unittest.TestCase):
+    def setUp(self):
+        # un-sorted case
+        self.collection1 = [5,3,4,6,7]
+        self.item1 = 4
+        # sorted case, result exists
+        self.collection2 = [10,30,40,45,50,66,77,93]
+        self.item2 = 66
+        # sorted case, result doesn't exist
+        self.collection3 = [10,30,40,45,50,66,77,93]
+        self.item3 = 67
+        # equal elements case, result exists
+        self.collection4 = [10,10,10,10,10]
+        self.item4 = 10
+        # equal elements case, result doesn't exist
+        self.collection5 = [10,10,10,10,10]
+        self.item5 = 3
+        # 1 element case, result exists
+        self.collection6 = [10]
+        self.item6 = 10
+        # 1 element case, result doesn't exists
+        self.collection7 = [10]
+        self.item7 = 1
+
+    def tearDown(self):
+        pass
+
+    def test_interpolation_search(self):
+        self.assertEqual(interpolation_search(self.collection1, self.item1), None)
+        
+        self.assertEqual(interpolation_search(self.collection2, self.item2), self.collection2.index(self.item2))
+        
+        self.assertEqual(interpolation_search(self.collection3, self.item3), None)
+        
+        self.assertEqual(interpolation_search(self.collection4, self.item4), self.collection4.index(self.item4))
+
+        self.assertEqual(interpolation_search(self.collection5, self.item5), None)
+        
+        self.assertEqual(interpolation_search(self.collection6, self.item6), self.collection6.index(self.item6))
+        
+        self.assertEqual(interpolation_search(self.collection7, self.item7), None)
+        
+
+
+class Test_interpolation_search_by_recursion(unittest.TestCase):
+    def setUp(self):
+        # un-sorted case
+        self.collection1 = [5,3,4,6,7]
+        self.item1 = 4
+        # sorted case, result exists
+        self.collection2 = [10,30,40,45,50,66,77,93]
+        self.item2 = 66
+        # sorted case, result doesn't exist
+        self.collection3 = [10,30,40,45,50,66,77,93]
+        self.item3 = 67
+        # equal elements case, result exists
+        self.collection4 = [10,10,10,10,10]
+        self.item4 = 10
+        # equal elements case, result doesn't exist
+        self.collection5 = [10,10,10,10,10]
+        self.item5 = 3
+        # 1 element case, result exists
+        self.collection6 = [10]
+        self.item6 = 10
+        # 1 element case, result doesn't exists
+        self.collection7 = [10]
+        self.item7 = 1
+
+    def tearDown(self):
+        pass
+
+    def test_interpolation_search_by_recursion(self):
+        self.assertEqual(interpolation_search_by_recursion(self.collection1, self.item1, 0, len(self.collection1)-1), None)
+        
+        self.assertEqual(interpolation_search_by_recursion(self.collection2, self.item2, 0, len(self.collection2)-1), self.collection2.index(self.item2))
+        
+        self.assertEqual(interpolation_search_by_recursion(self.collection3, self.item3, 0, len(self.collection3)-1), None)
+        
+        self.assertEqual(interpolation_search_by_recursion(self.collection4, self.item4, 0, len(self.collection4)-1), self.collection4.index(self.item4))
+
+        self.assertEqual(interpolation_search_by_recursion(self.collection5, self.item5, 0, len(self.collection5)-1), None)
+        
+        self.assertEqual(interpolation_search_by_recursion(self.collection6, self.item6, 0, len(self.collection6)-1), self.collection6.index(self.item6))
+        
+        self.assertEqual(interpolation_search_by_recursion(self.collection7, self.item7, 0, len(self.collection7)-1), None)
+ 
+
+
+if __name__ == '__main__':
+    unittest.main()