How to use pytest.approx() with syrupy

We have a bunch of tests that perform computations using pandas, numpy, and other scientific libraries and produce a dictionary containing the resulting key-value pairs. Some of the values are slightly different when run on different platforms (i.e. macOS vs Linux), so we wrap those values with pytest.approx() to accommodate those minor and acceptable differences.

Digging into the syrupy code, the final comparison between the test value and the snapshot is performed against serialized data, so it appears that pytest.approx() cannot be used. Is that correct? Or can you suggest a way to allow these two great features to be used together?

Thanks!

[hashstat]

Thanks for all your suggestions. I was able to solve the issue by rounding the numbers to a reasonable precision before comparison.

def test_snapshot(snapshot):
    computed = compute_pi()
    assert snapshot == round(computed, 8)

And all is working as expected.

# name: test_snapshot
  3.14159265
---

[iamogbz]

@hashstat it seems like when comparing you could approximate pi and use that compare against the computed value and then you can use a syrupy matcher to check and replace the matched value with the constant pi approximation.

Basically what @noahnu suggested but using matchers instead of a custom extension to make it terser.

import os
import pytest

pi = 3.141592653589793

def compute_pi():
    return {
        'win32': 3.141592654,
        'darwin': 3.14159265359,
    }.get(os.environ.get('PLATFORM'), 3.1415926536897)

def test_not_equal():
    assert pi != compute_pi()

def test_approx():
    assert pytest.approx(pi) == compute_pi()


def test_snapshot(snapshot):
    computed = compute_pi()
    approximated = pytest.approx(pi)
    def pi_approx_matcher(data, path):
        return approximated if data == approximated else data
    assert snapshot(matcher=pi_approx_matcher) == computed

Using your example

# name: test_snapshot
  3.141592653589793 ± 3.1e-06
---

$ PLATFORM=win32 pytest test_pi.py
test_pi.py ...                                                           [100%]
--------------------------- snapshot report summary --------------------------- 
1 snapshot passed.
============================== 3 passed in 0.03s ==============================