Snippet

Custom TestCase Mixin for Programmatic SQL Query Count Assertions

By subclassing Django's `CaptureQueriesContext`, you can write custom test mixins that measure executed database queries and fail unit tests dynamically when query boundaries are exceeded.

snippet.py

python

from django.test import TestCase
from django.test.utils import CaptureQueriesContext
from django.db import connection
 
class AssertQueryLimitMixin:
    def assert_max_queries(self, limit: int):
        class QueryContextManager(CaptureQueriesContext):
            def __exit__(self, exc_type, exc_val, exc_tb):
                super().__exit__(exc_type, exc_val, exc_tb)
                query_count = len(self.captured_queries)
                if query_count > limit:
                    raise AssertionError(f'Query limit exceeded: {query_count} > {limit}')
        return QueryContextManager(connection)

django

Breakdown

class AssertQueryLimitMixin:

Defines a reusable test mixin for database query boundary inspection.

class QueryContextManager(CaptureQueriesContext):

Extends Django SQL query capturing context manager.

if query_count > limit:

Compares the total captured SQL queries against the specified threshold and raises an AssertionError if exceeded.

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Custom TestCase Mixin for Programmatic SQL Query Count Assertions

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