I'm using Pytest to test some SQL queries my team runs programmatically over time.
My SQL queries are lists of JSONs - one JSON corresponds to one row of data.
I've got a function that diffs the JSON key:value pairs so that we can point to exactly which values are different for a given row. Ideally, I'd output a list of these diffs instead of the standard output of an assert statement, which ends up looking clunky and not-very-useful for the end user.
Pytest give us the hook pytest_assertrepr_compare to add a custom explanation about why an assertion failed.
You can create a class to wrap the JSON string and implement your comparator algorithm overloading the equal operator.
class JSONComparator:
def __init__(self, lst):
self.value = value
def __eq__(self, other):
# Here your algorithm to compare two JSON strings
...
# If they are different, save that information
# We will need it later
self.diff = "..."
return True
# Put the hook in conftest.py or import it in order to make pytest aware of the hook.
def pytest_assertrepr_compare(config, op, left, right):
if isinstance(left, JSONComparator) and op == "==":
# Return the diff inside an array.
return [left.diff]
# Create a reference as an alias if you want
compare = JSONComparator
def test_somethig():
original = '{"cartoon": "bugs"}'
expected = '{"cartoon": "bugs"}'
assert compare(original) == expected