fix(fscheck): apply Verbose, QuietOnSuccess and Parallelism; validate Replay

[JesseKlaasse]

Description

FsCheckPropertyAttribute exposes Verbose, QuietOnSuccess and Parallelism, and the docs list the first two, but FsCheckPropertyTestExecutor.CreateConfig never passed them to FsCheck. All three did nothing. For example, every passing property printed Ok, passed 100 tests., even with QuietOnSuccess = true.

• Verbose: the base config is now Config.VerboseThrowOnFailure instead of QuickThrowOnFailure. It uses the same throwing runner and adds output for each argument and each shrink.
• QuietOnSuccess: WithQuietOnSuccess.
• Parallelism: a ParallelRunConfig is set only when the value is above 1. FsCheck switches to its thread-pool runner for any ParallelRunConfig, even with degree 1, so the default (1) stays on the sequential path.

Replay parsing was also broken:

• "12345" (seed only) produced gamma 0, which throws ArgumentException: Gamma must be odd, given: 0.
• "abc,1" was silently ignored, and the test ran with a random seed.
• FsCheck's own hint, Replay directly at failing step with (seed,gamma,size), was dropped as well: with the parentheses the whole value was ignored, and without them the size was lost.

Replay now accepts what FsCheck reports: "seed,gamma" replays the whole run and "seed,gamma,size" replays only the failing step, with or without parentheses. Any other value fails the test with a message that lists both formats.

Why a lone seed is rejected instead of getting a default gamma: FsCheck has a golden-gamma default (new Rnd(seed)). But FsCheck never reports a seed without its gamma, and the same seed with a different gamma generates a different run. A default gamma would therefore quietly replay a run that is not the one that failed. FsCheck.Xunit's PropertyAttribute handles this the same way: it requires seed and gamma, accepts an optional size and trims the parentheses. A lone seed always threw before this change, so no working usage breaks.

Related Issue

None filed.

Type of Change

• Bug fix (non-breaking change that fixes an issue)

Tests

• tests/TUnit.UnitTests/FsCheckPropertyConfigTests.cs (run by CI) covers:

  • how each option maps to Config;
  • that Verbose still throws on failure;
  • which Replay values are accepted and which are rejected.

  To make this testable, CreateConfig is now internal, and TUnit.FsCheck has InternalsVisibleTo TUnit.UnitTests, the same setup as TUnit.Playwright.

• examples/TUnit.Example.FsCheck.TestProject/ConfigurationOptionTests.cs tests end to end through [FsCheckProperty], next to the existing CancellationTokenBehaviourTests. It covers:

  • captured output with default settings, with QuietOnSuccess and with Verbose;
  • overlapping invocations with Parallelism = 4;
  • a (seed,gamma,size) replay that runs exactly one invocation.

  On main, the four option tests fail and the default-output control test passes. The pipeline builds this project but does not run it, which is why the unit tests above exist.

• Mutation check: I tried 8 single-line mutants of the change (for example: drop WithQuietOnSuccess, use the non-throwing Config.Verbose, start parallelism at 1, drop the size, allow an even gamma, skip trimming the parentheses). The unit tests catch each one.

• Ran locally:

  • TUnit.FsCheck Release build with ContinuousIntegrationBuild=true for netstandard2.0, net8.0, net9.0 and net10.0: no new warnings.
  • Example project (22 tests) and the new unit tests (23): green on net8.0, net9.0 and net10.0.
  • Full TUnit.UnitTests suite: green on net10.0.

Not affected: discovery and execution modes, generator snapshots and public API (CreateConfig only went from private to internal). No new reflection.

Docs

docs/docs/examples/fscheck.md:

• The options table now includes Parallelism.
• The Reproducing Failures section describes both Replay formats.

The old example, Replay = "12345,67890", had an even gamma and would have thrown. I did not run Verify-DocSnippets.ps1 locally. The only change inside a code block is the Replay string.

Additional Notes

TUnit behaviour I noticed while writing the example tests: FsCheck writes with printf, i.e. TextWriter.Write without WriteLine. TUnit buffers such partial lines per test and only routes them on flush, which happens after the [After(Test)] hooks. Inside such a hook, TestContext.GetStandardOutput() therefore misses that output until Console.Out is flushed, so the example hooks flush it first. This PR does not change that behaviour.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes

  • FsCheck replay settings support seed,gamma to replay a full run and seed,gamma,size to replay a failing step. Invalid formats fail with an explanation.
  • Parallel execution runs sequentially when the setting is below 2; higher values enable parallel runs.

• Documentation

  • Clarified replay formats, verbose output, success summaries, and thread-safety requirements for parallel execution.

[coderabbitai]

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Reviewing files that changed from the base of the PR and between 284db9b and 2d8211c.

📒 Files selected for processing (2)

• src/TUnit.FsCheck/FsCheckPropertyTestExecutor.cs
• tests/TUnit.UnitTests/FsCheckPropertyConfigTests.cs

🚧 Files skipped from review as they are similar to previous changes (2)

• src/TUnit.FsCheck/FsCheckPropertyTestExecutor.cs
• tests/TUnit.UnitTests/FsCheckPropertyConfigTests.cs

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📝 Walkthrough

Walkthrough

The FsCheck executor applies output and parallelism options and parses replay values with a seed, gamma, and optional size. Documentation and unit and example tests cover these configuration behaviors.

Changes

FsCheck Configuration

Layer / File(s)	Summary
Configuration behavior and replay parsing src/TUnit.FsCheck/FsCheckPropertyAttribute.cs, src/TUnit.FsCheck/FsCheckPropertyTestExecutor.cs, docs/docs/examples/fscheck.md	The executor applies verbose, quiet-on-success, parallelism, and replay settings. Replay accepts two or three comma-separated values, with optional surrounding parentheses, an unsigned seed and odd gamma, and an optional nonnegative size. The documentation describes the supported formats and options.
Configuration unit tests src/TUnit.FsCheck/TUnit.FsCheck.csproj, tests/TUnit.UnitTests/*	Unit tests cover defaults, output settings, parallelism, and replay parsing. The test project references TUnit.FsCheck, which grants it internal access.
Runtime option tests examples/TUnit.Example.FsCheck.TestProject/ConfigurationOptionTests.cs	Example tests check FsCheck output, parallel invocations, and replay with a size. The output helper flushes standard output before reading captured output.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 2d821

This change makes the documented FsCheck options take effect and makes replay parsing stricter. Tests cover the new behavior, and no merge-blocking risk was identified.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 15.38% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 26 functions across 4 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main changes: applying FsCheck options and validating Replay values.
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 checks the seed and gamma,
Then watches test reports unfold.
Five small runs hop through the output,
While parallel paws keep time.
A replay brings one step back,
And quiet leaves the page calm.}

_{Comment @coderabbitai help to get the list of available commands.}

[github-actions]

Review

I found no blocking issues. The change does what the description says.

• Options: Verbose, QuietOnSuccess and Parallelism are now passed to FsCheck. Using VerboseThrowOnFailure keeps failures throwing. Setting ParallelRunConfig only when Parallelism > 1 keeps the default on the sequential path.
• Replay: the parser is strict and its error message lists both accepted formats. It accepts seed,gamma and seed,gamma,size, with or without parentheses. Rejecting a lone seed is the right call, because a default gamma would quietly replay a different run. Using NumberStyles.None with the invariant culture rejects negative values, and the odd-gamma check gives a clear error up front.
• Tests: the unit tests cover the option-to-Config mapping and the accept/reject cases for Replay. The end-to-end tests cover output, parallelism and replay-with-size. The InternalsVisibleTo setup matches the one used for TUnit.Playwright.

Nits, not blocking:

• Trim('(', ')') also accepts unbalanced input such as (123,45. That is harmless, but a stricter check would be more consistent with the rest of the validation.
• ParallelismTests waits up to 10 seconds on a thread-pool dependency. It only takes that long if parallelism is broken, so this is acceptable.

Looks good to merge.

[greptile-apps]

Confidence Score: 5/5

[Medium impact] The PR appears safe to merge; the previous replay parsing issue is fixed.

Summary

The PR applies Verbose, QuietOnSuccess, and Parallelism to FsCheck and validates both supported Replay formats.

• The latest change fixes the previous finding by removing only one matching pair of parentheses.
• Four new test cases cover unmatched and repeated parentheses.
• No new actionable issues were found.

_{Reviews (2) · Last reviewed commit: "fix(fscheck): reject unbalanced parenthe..." · Reviewed by Greptile}

[coderabbitai]

Actionable comments posted: 1

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Inline comments:
Review comments at @src/TUnit.FsCheck/FsCheckPropertyTestExecutor.cs:
- Line 141: Update replay parsing in FsCheckPropertyTestExecutor to remove
exactly one outer pair only when both parentheses are present, and reject
unmatched or repeated parentheses with the documented format error before
splitting the replay value.

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📒 Files selected for processing (7)

• docs/docs/examples/fscheck.md
• examples/TUnit.Example.FsCheck.TestProject/ConfigurationOptionTests.cs
• src/TUnit.FsCheck/FsCheckPropertyAttribute.cs
• src/TUnit.FsCheck/FsCheckPropertyTestExecutor.cs
• src/TUnit.FsCheck/TUnit.FsCheck.csproj
• tests/TUnit.UnitTests/FsCheckPropertyConfigTests.cs
• tests/TUnit.UnitTests/TUnit.UnitTests.csproj

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[thomhurst]

Thanks @JesseKlaasse - could you take a look at the replay concerns above?

[JesseKlaasse]

Done in 2d8211c: Replay now strips exactly one enclosing pair of parentheses, so unbalanced or repeated ones fail with the format error instead of running. I left the 10-second wait in ParallelismTests as is, since it is only reached when parallelism is broken.

[github-actions]

Review

This is a solid bug fix. I read the diff only and did not run the tests.

• Option wiring: Verbose, QuietOnSuccess and Parallelism now reach FsCheck. VerboseThrowOnFailure keeps the throwing behaviour, and a test covers that. Only Parallelism > 1 sets a ParallelRunConfig, which avoids switching a default run onto FsCheck's thread-pool runner.
• Replay parsing: It is strict and fails loudly instead of silently running with a random seed. Rejecting a lone seed is the right call, since a default gamma would replay a different run than the one that failed. The explanation in the PR and the error message is clear. Checking that gamma is odd up front gives a better error than FsCheck's ArgumentException.
• Tests: Unit tests cover the config mapping and a good range of valid and invalid Replay values. The end-to-end example tests check observable behaviour: captured output, overlapping invocations, and single-step replay.
• Design: InternalsVisibleTo on CreateConfig follows the existing Playwright setup.

Two minor, non-blocking points:

1. ParallelismTests waits up to 10s for the overlap and counts timeouts, so a very constrained thread pool could make it slow. It is deterministic enough, so I would leave it as is.
2. An out-of-range size or seed is rejected with the generic message, which is fine.

LGTM.

[thomhurst]

Thanks @JesseKlaasse !