test(flags): make wrong-key load_feature_flags deterministic

[andehen]

Summary

Stabilize feature-flag tests in CI and remove runtime-dependent behavior in capture cache handling.

Example failure run where 3.10 and 11 passes, but 13 and 14 fails https://github.com/PostHog/posthog-python/actions/runs/21986040963/job/63520352185?pr=431

Changes

• Make test_load_feature_flags_wrong_key deterministic by mocking posthog.client.get to raise APIError(401, "Unauthorized") and mocking posthog.client.Poller.
• Make test_capture_multiple_users_doesnt_out_of_memory deterministic by setting client.distinct_ids_feature_flags_reported.max_size = 100 directly on the instance (with an explanatory comment).
• Update Client._capture_feature_flag_called to avoid implicit defaultdict missing-key insertion and use explicit get/assign before adding reported flag keys.

Why

CI reproduced a non-deterministic failure in capture-cache size assertions (101 != 1) that did not consistently reproduce locally. These changes remove reliance on runtime-specific insertion behavior and network-dependent test setup.

Validation

• pytest -q posthog/test/test_feature_flags.py -k "test_load_feature_flags_wrong_key"
• pytest -q posthog/test/test_feature_flags.py -k "test_capture_multiple_users_doesnt_out_of_memory"
• pytest -q posthog/test/test_feature_flags.py -k "TestCaptureCalls"

[github-actions]

posthog-python Compliance Report

Date: 2026-02-13 13:43:18 UTC
Duration: 159369ms

✅ All Tests Passed!

29/29 tests passed

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Capture Tests

✅ 29/29 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	517ms
Format Validation.Event Has Uuid	✅	1507ms
Format Validation.Event Has Lib Properties	✅	1507ms
Format Validation.Distinct Id Is String	✅	1506ms
Format Validation.Token Is Present	✅	1507ms
Format Validation.Custom Properties Preserved	✅	1507ms
Format Validation.Event Has Timestamp	✅	1507ms
Retry Behavior.Retries On 503	✅	9514ms
Retry Behavior.Does Not Retry On 400	✅	3510ms
Retry Behavior.Does Not Retry On 401	✅	3507ms
Retry Behavior.Respects Retry After Header	✅	9514ms
Retry Behavior.Implements Backoff	✅	23520ms
Retry Behavior.Retries On 500	✅	7509ms
Retry Behavior.Retries On 502	✅	7514ms
Retry Behavior.Retries On 504	✅	7513ms
Retry Behavior.Max Retries Respected	✅	23528ms
Deduplication.Generates Unique Uuids	✅	1497ms
Deduplication.Preserves Uuid On Retry	✅	7514ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	14513ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	7516ms
Deduplication.No Duplicate Events In Batch	✅	1503ms
Deduplication.Different Events Have Different Uuids	✅	1506ms
Compression.Sends Gzip When Enabled	✅	1507ms
Batch Format.Uses Proper Batch Structure	✅	1507ms
Batch Format.Flush With No Events Sends Nothing	✅	1005ms
Batch Format.Multiple Events Batched Together	✅	1505ms
Error Handling.Does Not Retry On 403	✅	3508ms
Error Handling.Does Not Retry On 413	✅	3508ms
Error Handling.Retries On 408	✅	7514ms

[andehen]

@greptile-apps please review