[DB-1951] Add MSA idempotency tests that correspond to the existing behaviour

[timothycoleman]

These are probably largely covered by tests elsewhere, but I wanted to have a systematic approach in one place. It'll make it easier to verify the effect of adjusting the idempotency behaviour of check-only streams

[qodo-code-review]

Review Summary by Qodo

Add comprehensive MSA idempotency tests for multi-stream writes

🧪 Tests

Walkthroughs

Description

• Add comprehensive idempotency test suite for multi-stream writes
• Test Full, Partial, WithFailedCheck, and WithSuccessfulCheck idempotency scenarios
• Test idempotent behavior across different expected versions and stream states
• Test idempotent behavior when stream is modified after initial write

Diagram

flowchart LR
  A["Test Suite Setup"] --> B["IdempotencyKind Enum"]
  B --> C["IdempotentBehaviorByKindCases"]
  C --> D["idempotent_behaviour_by_kind Test"]
  B --> E["StreamModification Enum"]
  E --> F["IdempotentBehaviorByStreamChangedCases"]
  F --> G["idempotent_behavior_by_stream_change Test"]

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File Changes

1. src/KurrentDB.Core.XUnit.Tests/TransactionLog/MultiStreamWrites/MultiStreamWritesTests.cs 🧪 Tests +305/-0

Add systematic idempotency test coverage for multi-stream writes

• Added IdempotencyKind enum with Full, Partial, WithFailedCheck, and WithSuccessfulCheck variants
• Added IdempotentBehaviorByKindCases() theory data with 40+ test cases covering different
 expected versions and stream states
• Added idempotent_behaviour_by_kind() test method validating idempotency behavior for each kind
• Added StreamModification enum and IdempotentBehaviorByStreamChangedCases() theory data with
 15+ test cases
• Added idempotent_behavior_by_stream_change() test method validating idempotency when streams are
 modified

src/KurrentDB.Core.XUnit.Tests/TransactionLog/MultiStreamWrites/MultiStreamWritesTests.cs

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Code Review by Qodo

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[Copilot]

Pull request overview

Adds a systematic set of multi-stream append idempotency tests to capture and lock in current behavior, especially around check-only streams and stream-state transitions, making future behavior changes easier to validate.

Changes:

• Introduces theory-driven test matrices for idempotent retries by “kind” (full/partial + check-only variants).
• Adds theory-driven tests for idempotent retries when the target stream changes between attempts (more events / soft-delete / tombstone).
• Introduces supporting enums and case tables to enumerate applicable (ExpectedVersion, StreamState) combinations.

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[Copilot]

For non-success retries, this test only asserts retry.Result. Other tests in this file also assert ConsistencyCheckFailures (and often FirstEventNumbers/LastEventNumbers) to verify which stream failed and why. Adding those assertions here would make these idempotency cases much more specific and prevent regressions where the error shifts from T to the check-only stream (or vice versa).

[linear]

DB-1951 Adjust idempotency for check-only streams