test.py

import io
import sys
sys.stdout = buffer = io.StringIO()

# from app import my_function
import pytest
import app
import re
import os

@pytest.mark.it("You should declare a function named sing()")
def test_function_sing_exists(app):
    try:
        assert app.sing
    except AttributeError:
        raise AttributeError("The function 'sing' should exist on app.py")

@pytest.mark.it("You should not be hard coding the output")
def test_function_hardcode_output():
    path = os.path.dirname(os.path.abspath(__file__))+'/app.py'
    with open(path, 'r') as content_file:
        content = content_file.read()
        regex = re.compile(r"\breturn\s*[^\"][a-zA-Z0-9]*\b\s*")
        assert bool(regex.search(content)) == True

@pytest.mark.it("The function sing() should return a string with the song lyrics")
def test_function_sing_exists(app):
    try:
        assert app.sing() == " nlet it be,\nlet it be,\nthere will be an answer,\nlet it be,\nlet it be,\nlet it be,\nlet it be,\nlet it be,\nwhisper words of wisdom, let it be"
    except AttributeError:
        raise AttributeError("The function 'sing' should exist on app.py")