Better diffs in pytest

How often do you compare dictionaries in (unit) tests? How do you handle diff outputs to make them as readable as possible?

Let’s create a simple test.

def test_diff():
    assert {"x": 1} == {"x": 2}

The default test summary looks like this:

Pytest Diff

The dictionaries are very small so we can see the difference without any issues. What if the dictionaries are bigger? Look at this example.

from faker import Faker

fake = Faker()
dict_1 = fake.pydict(nb_elements=10)
dict_2 = dict_1.copy()
dict_2[list(dict_1.keys())[1]] = "Test 1"
dict_2[list(dict_1.keys())[2]] = "Test 2"
dict_2[list(dict_1.keys())[3]] = "Test 3"
dict_2[list(dict_1.keys())[5]] = "Test 4"
dict_2[list(dict_1.keys())[6]] = "Test 5"


def test_diff():
    assert dict_1 == dict_2

The result.

pytest-dictsdiff

It gives you information about differences between both dictionaries, line by line. It looks better than the default diffs but I would like to present a better option.

pytest-icdiff

My favorite solution, pytest-icdiff. It displays a better diff summary and we don’t need additional code!

Look at this. Use the same example as at the beginning.

from faker import Faker

fake = Faker()
dict_1 = fake.pydict(nb_elements=10)
dict_2 = dict_1.copy()
dict_2[list(dict_1.keys())[1]] = "Test 1"
dict_2[list(dict_1.keys())[2]] = "Test 2"
dict_2[list(dict_1.keys())[3]] = "Test 3"
dict_2[list(dict_1.keys())[5]] = "Test 4"
dict_2[list(dict_1.keys())[6]] = "Test 5"


def test_diff():
    assert dict_1 == dict_2

The result.

pytest-icdiff

Let’s try to use -vv option.

pytest-icdiff-vv

How about you? Do you know better options?