Struggling To Understand These 2 Python Files

[samlee916]

Please help me understand the code and its output

Find the missing element:
Given a sorted list or array, find a more efficient way to identify the element that is missing.
Below are code snippets from two files (findMissing.py and findMissingTest.py), create a
directory with these files and code snippets in them. If you run “python -m unittest
findMissingTest” from terminal or cmd you should see the test fail. Modify the function in
“findMissing.py” to make the test pass.
findMissing.py

#the idea here was to get mid of the array
#now if the distance of mid from starting is not equal to distance of starting, 
#it means missing element is left side
#similarly it may be on right side
#if not the case in both the answer will be no missing element
def findMissing(arr):
    #get start index
    start = 0
    #get end index
    end = len(arr) - 1
    #get mid
    mid = 0
    #loop until start +1 is less than end
    while (start + 1 < end): 
       #floor division
        mid = (start + end) // 2
        #If the missing number is less than mid, go through the left side
        if (arr[start] - start) != (arr[mid] - mid): 
            end = mid 
        #else missing number is on the right side
        elif (arr[end] - end) != (arr[mid] - mid): 
            start = mid
        if(start + 1 == end):
            return arr[mid] + 1
    raise ValueError(msg = "No missing element")

findMissingTest.py

import unittest
from timeit import default_timer
from sys import version_info
from findMissing import findMissing
class StringCalculatorTests(unittest.TestCase):
    def test_findMissing(self):
        missing = 60000123
        print("Missing element actual : "+str(missing))
        arr = list(range(100000000))
        arr.remove(missing)
        start_time = default_timer()
        result = findMissing(arr)
        end_time = default_timer()
        print("Algo Missing element : "+str(result))
        print("Time took to find missing element is : %15f"%(end_time-start_time)+" seconds")
        if version_info.major == 2:
            self.assertGreater(2, end_time - start_time)
        elif version_info.major == 3:
            self.assertGreater(2.5, end_time - start_time)
            self.assertEqual(missing, result)

Output:
PS C:\Users\slee5\Desktop\Code> python -m unittest findMissingTest.py
Missing element actual : 60000123
Algo Missing element : 60000123
Time took to find missing element is : 0.008799 seconds
.
----------------------------------------------------------------------
Ran 1 test in 25.192s

OK
PS C:\Users\slee5\Desktop\Code>

[Gribouillis]

The idea is easy to understand, take the list

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

If you remove 0, 1, 2, 3 or 4, then L[4] has value 5. On the other hand, if you remove 5, 6, 7, 8 or 9, then L[4] has value 4. Hence by checking the value of L[4], you can say if the missing value is in range(0, 5) or in range(5, 10). The algorithm then repeats the same argument for the subarrays.

[ndc85430]

It looks like the test is already passing. The output doesn't show a failure.