Will try to implement the second order difference equation formula for this problem.

Euler Project #2.py

import unittest

def EvenFibonacciNumbers(limit):
    #Find all even fibonacci numbers
    fibonacciSeries = FibonacciGenerator(limit)
    return sum(i for i in fibonacciSeries if i % 2 == 0)
    
def FibonacciGenerator(limit):
    a = 0
    b = 1
    yield a
    while True:
        tmp = a+b
        yield tmp
        a = b
        b = tmp
        if tmp > limit:
            break
class Test(unittest.TestCase):
    def test_EvenFibonacciNumbers(self):
        self.assertEqual(EvenFibonacciNumbers(10),10)

if __name__ == '__main__':
    unittest.main(exit=False)
    print(EvenFibonacciNumbers(4000000))

Used the generator directly in the list comprehension and move the logic of limiting the length of fibonacci series to the generator.