Add fakesnow module

[anjeongkyun]

Adds fakesnow, a local Snowflake fake backed by DuckDB. The official snowflake-jdbc driver connects to it unmodified, so JVM projects can test VARIANT, LATERAL FLATTEN and QUALIFY without a Snowflake account or a paid emulator.

The Java module is at anjeongkyun/testcontainers-fakesnow (Apache-2.0), published as io.github.anjeongkyun:testcontainers-fakesnow:0.1.0. I maintain it.

[anjeongkyun]

Bumped the entry to 0.1.2, which is the current release.

Since opening this the module has picked up a few things worth mentioning: it now defaults to fakesnow 0.11.15, and the compatibility probe in its tests covers batch inserts, setTimestamp binding, getPrimaryKeys and prepared statement side effects, with the versions each needs. Several of those work because of fixes that went upstream into fakesnow itself, so the module and the fake have been moving together.

No rush on my side, just flagging that it's still current if it's useful to have in the registry.

[coderabbitai]

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Summary by CodeRabbit

• Documentation
  • Added documentation for the community-maintained Fakesnow Testcontainers module.
  • Included setup instructions, Maven dependency details, and a usage example for Java projects.
  • Documented local testing of Snowflake-style SQL, including VARIANT, LATERAL FLATTEN, and QUALIFY, without requiring access to a Snowflake account.
  • Clarified that the Snowflake JDBC driver connects to the local service without modification.

Walkthrough

The change adds a fakesnow module entry to the index. The entry documents Java usage, Maven dependencies, and DuckDB-backed Snowflake-compatible behavior.

Changes

fakesnow module

Layer / File(s)	Summary
Module index entry modules/fakesnow/index.md	Adds the fakesnow relational-database entry with repository information, a Testcontainers usage example, Maven dependencies, and module behavior details.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~2 minutes

Change: Feature

Merge Risk: ⚪ Minimal · up to 38153

The documented dependency is available and no actionable risk remains.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely identifies the main change: adding the fakesnow module.
Description check	✅ Passed	The description directly explains the fakesnow module, its Snowflake emulation purpose, supported SQL features, dependency, and maintenance details.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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_{A rabbit finds a module bright
With Snowflake queries set just right
DuckDB hums in a tiny den
Maven brings the tests back in
VARIANT hops through code tonight}

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[coderabbitai]

Actionable comments posted: 1

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Inline comments:
In `@modules/fakesnow/index.md`:
- Around line 16-21: Update the dependency documentation around the
testcontainers-fakesnow Maven snippet to explicitly require the snowflake-jdbc
driver, either by adding its dependency declaration or clearly stating that
consumers must add it separately.

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[anjeongkyun]

@mdelapenya could you take a look when you get a chance? It is one file and no code, just the fakesnow entry in the Java module list.

I think it slipped past triage rather than being held for a reason: #193 was opened two weeks after this one and merged the next day. Nothing here has gone stale either, the entry points at 0.1.2 which is still the current release on Maven Central.

Happy to rebase or reword if the entry format has changed since August.

[mdelapenya]

Sorry for the delay, will take a look at this now

[mdelapenya]

BTW @anjeongkyun would you be interested in building a Go flavor for your module? I'm the Go maintainer, so I'd be very happy to see it ported to Go and/or other languages. WDYT ?

[mdelapenya]

LGTM thanks for your contribution and sorry again for the time it took to get merged 🙏

[anjeongkyun]

Thanks for merging it.

I'm interested. A Go flavor makes sense here since fakesnow's server mode is meant for connectors from any language, not just Python. Before I commit to it I want to check that gosnowflake talks to fakesnow the way snowflake-jdbc does. The REST paths line up (/session/v1/login-request, /queries/v1/query-request) but I have not actually run it yet, and the JVM module needed a couple of fakesnow fixes before it worked, so I would rather find out first than promise and stall.

I will report back either way. If it does work, would modules/fakesnow in testcontainers-go be the right home, next to fakegcsserver?

[anjeongkyun]

Checked it, gosnowflake does talk to fakesnow. 13 of the 14 things I tried work unchanged, including the Snowflake-specific ones the Java module exists for: VARIANT via PARSE_JSON(...):k[1], LATERAL FLATTEN, QUALIFY, MERGE, multi-row scans.

The one that failed was transactions. database/sql sends BEGIN from Tx.Begin, and that came back with Catalog Error: Table with name BEGIN does not exist!. The statement itself ran fine; the server then issued DESCRIBE BEGIN to read the result metadata and duckdb took that as a request to describe a table called BEGIN. In-process patching was unaffected, so it only showed up for clients going through the HTTP server, which is every non-Python one. Fixed in tekumara/fakesnow#444, merged earlier today. db.Begin(), insert, Rollback() now works end to end.

So I'm up for the Go module. One thing worth waiting on: the fix is on main but not released, and the published images trail the releases a little (newest tag on ghcr is 0.11.18 while the release is 0.11.20). I would rather pin the module to an image that has the fix than ship one where transactions fail.

Still not sure where it belongs. Would modules/fakesnow in testcontainers-go, next to fakegcsserver, be right?

[mdelapenya]

@anjeongkyun yeah, you can add it under the Go project, or host it yourself, whatever that works. If you add it to Go, please update the docs accordingly, following the rest of the modules' docs 🙏