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feat(checks): add prints expectations (#2742) - #2743

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Sep 18, 2026
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feat(checks): add prints expectations (#2742)#2743
natebosch merged 6 commits into
dart-lang:masterfrom
kevmoo:checks-prints

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@kevmoo kevmoo commented Aug 30, 2026 •
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Add prints() check extensions on Subject<void Function()> (FunctionPrints) and Subject<Future<void> Function()> (AsyncFunctionPrints) to validate captured print() output from synchronous and asynchronous callbacks.

  • Intercept print() via ZoneSpecification during function execution.
  • FunctionPrints.prints() (on Subject<void Function()>) returns Subject<String> for synchronous checking on captured output and asserts that the callback does not return a Future at runtime.
  • AsyncFunctionPrints.prints() (on Subject<Future<void> Function()>) awaits the returned Future before checking Condition<String> and returning Future<Subject<String>>.
  • Add runnable {@example} files, update migration guide, and add tests for output capture and error rejections.

Closes #2742

@kevmoo
feat(checks): add prints and printsAsync expectations (dart-lang#2742)
fdef0ca 
Add prints() and printsAsync() check extensions on Subject<T Function()> to validate captured stdout output from synchronous and asynchronous callbacks.

- Intercept print() via ZoneSpecification during function execution.
- prints() returns Subject<String> for synchronous checking on captured output.
- printsAsync() waits for the returned Future before checking AsyncCondition<String>.
- Update migration guide and add tests for output capture and error rejections.

Closes dart-lang#2742
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kevmoo requested a review from a team as a code owner August 30, 2026 20:17
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kevmoo requested a review from natebosch August 30, 2026 20:17
@github-actions github-actions Bot added the package:checks Issues related to pkg:checks label Aug 30, 2026
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github-actions Bot commented Sep 10, 2026

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@natebosch

natebosch commented Sep 11, 2026

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I took some time this afternoon to put some thought into this and the expectAsync APIs. I think I'm leaning towards the idea that these things shouldn't be coupled to the testing APIs directly, we should consider separating them out into a different package. I've had gemini write a rough draft at #2755 - I think we can have some discussion about the API and decide whether or not to work towards cleaning that up or landing this instead.

natebosch
natebosch requested changes Sep 18, 2026
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I think if we put one extension on Subject<void Function()> and another other Subject<Future<void> Function> then we can call them both prints. The one use case that design disallows is explicitly calling printAsync for a function reference that is statically typed as synchronous but is async in practice. I don't think that's a problem. Maybe the synchronous implementation can assert that it doesn't get a Future return value.

@kevmoo
feat(checks): overload prints on Subject<void Function()> and Subject…
cbc31fb 
…<Future<void> Function()>

- Merge origin/master and resolve CHANGELOG.md conflict
- Replace separate prints/printsAsync methods on FunctionChecks<T> with overloaded prints() extensions on Subject<void Function()> (FunctionPrints) and Subject<Future<void> Function()> (AsyncFunctionPrints)
- Assert that synchronous Subject<void Function()>.prints() does not receive a Future at runtime
- Add runnable @example files for both sync and async prints()
@kevmoo

kevmoo commented Sep 18, 2026

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@natebosch Done!

  • Replaced prints / printsAsync on FunctionChecks<T> with overloaded .prints() extensions on Subject<void Function()> (FunctionPrints) and Subject<Future<void> Function()> (AsyncFunctionPrints).
  • Added an assert(result is! Future, ...) in FunctionPrints.prints if a function statically typed as void Function() returns a Future at runtime.
  • Merged master and added runnable {@example} files (example/function/function/prints.dart and example/function/async_function/prints.dart).

PTAL!

@kevmoo kevmoo changed the title feat(checks): add prints and printsAsync expectations (#2742) feat(checks): add prints expectations (#2742) Sep 18, 2026
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kevmoo requested a review from natebosch September 18, 2026 07:12
@natebosch
natebosch merged commit f927df2 into dart-lang:master Sep 18, 2026
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kevmoo deleted the checks-prints branch September 22, 2026 05:05
copybara-service Bot pushed a commit to dart-lang/sdk that referenced this pull request Sep 22, 2026
@natebosch dart-scoped@luci-project-accounts.iam.gserviceaccount.com
[deps] rev dartdoc, ecosystem, http, native, shelf, test, tools
aaa7b10 
Revisions updated by `dart tools/rev_sdk_deps.dart`.

dartdoc (https://github.com/dart-lang/dartdoc/compare/df2f2cd..c68debc):
  c68debcb  Mon Sep 21 11:07:33 2026 +0200  Sarah Zakarias  Adapt the {@example} code fence to the example content (dart-lang/dartdoc#4285)

ecosystem (https://github.com/dart-lang/ecosystem/compare/1bdafd8..16dca7a):
  16dca7a  Mon Sep 21 08:04:10 2026 -0700  Kevin Moore  fix(firehose): keep dart_apitool crash details in logs and sanitize breaking table row (dart-lang/ecosystem#461)

http (https://github.com/dart-lang/http/compare/35769ba..d8e8e9c):
  d8e8e9c  Mon Sep 21 18:26:27 2026 +0900  DubaiChewyCookie  fix(http2): bound peer-controlled streams and headers (dart-lang/http#1958)
  286037b  Thu Sep 17 17:12:02 2026 -0700  Brian Quinlan  chore(http2): prepare to release 3.1.0 (dart-lang/http#1987)
  a067c94  Wed Sep 16 15:57:52 2026 -0700  Brian Quinlan  fix(cupertino_http): possible URLRequest memory leaks (dart-lang/http#1989)
  0d15438  Thu Sep 17 00:43:43 2026 +0300  Ellet  chore(ok_http): Built-in Kotlin and resolve AGP 9 warnings (dart-lang/http#1973)

native (https://github.com/dart-lang/native/compare/a88aaaf..f628b26):
  f628b26f0  Mon Sep 21 23:21:05 2026 +0200  Daco Harkes  [hooks] Add unit tests for `ProtocolExtension` defaults and `build`/`link` error paths (dart-lang/native#3668)
  474a93f39  Mon Sep 21 08:01:13 2026 +0500  Muhammad Anas Naveed  [jni][jnigen] Update Groovy Gradle property assignments (dart-lang/native#3678)
  4434b7f3c  Mon Sep 21 10:31:09 2026 +1000  Liam Appelbe  [jni] Ignore coverage of generated files (dart-lang/native#3665)
  b66dfdeae  Mon Sep 21 10:27:27 2026 +1000  Liam Appelbe  [objective_c] Use `objc_retainAutoreleasedReturnValue` (dart-lang/native#3664)
  541121b4b  Fri Sep 18 17:30:03 2026 +0200  Daco Harkes  [record_use] Add status and coverage badges to `README.md` (dart-lang/native#3675)
  b97663824  Fri Sep 18 17:25:10 2026 +0200  Daco Harkes  [hooks] Prepare `prebuilt_assets_example` v0.1.2 for release (dart-lang/native#3672)
  876145f0c  Fri Sep 18 15:23:34 2026 +0200  Daco Harkes  [hooks] Use `prebuilt/` instead of `assets/` in `prebuilt_assets_example` (dart-lang/native#3671)
  73bd0b7b3  Fri Sep 18 12:58:36 2026 +0200  Daco Harkes  [hooks] Prepare `prebuilt_assets_example` v0.1.1 for release (dart-lang/native#3669)
  4e0f1983f  Fri Sep 18 11:40:30 2026 +0200  Daco Harkes  [hooks] Add example for bundling prebuilt assets in `pub publish` (dart-lang/native#3637)
  22d7cf8da  Fri Sep 18 09:28:25 2026 +0200  Daco Harkes  [native_test_helpers] Add unit tests for `yamlToJson` and `findPackageRoot` (dart-lang/native#3662)
  74e631a8b  Fri Sep 18 09:28:25 2026 +0200  Daco Harkes  [hooks] Add unit tests for `link` API and `MetadataAsset` (dart-lang/native#3661)
  3428cb968  Fri Sep 18 09:28:24 2026 +0200  Daco Harkes  [data_assets] Add unit tests for `LinkOutput` data asset extensions (dart-lang/native#3660)
  0e4eea612  Fri Sep 18 09:28:24 2026 +0200  Daco Harkes  [code_assets] Add unit tests for `testCodeBuildHook` and `CCompilerConfig` (dart-lang/native#3659)
  dc44c5383  Fri Sep 18 09:28:24 2026 +0200  Daco Harkes  [ffi] Add unit tests for `Arena` error handling and `malloc.free` (dart-lang/native#3658)
  1e1e2fb8a  Fri Sep 18 09:28:23 2026 +0200  Daco Harkes  [native_toolchain_c] Default `linkerOptions` in `CLinker.run` and add `CLibrary` tests (dart-lang/native#3657)
  f3c066006  Fri Sep 18 09:28:23 2026 +0200  Daco Harkes  [data_assets] [hooks] [hooks_runner] [record_use] Add coverage ignore comments for debug methods (dart-lang/native#3656)
  59cd44422  Fri Sep 18 09:28:22 2026 +0200  Daco Harkes  [infra] Clean coverage directory and enable `--check-ignore` in `tool/ci.dart` (dart-lang/native#3655)
  b859d5fa8  Fri Sep 18 09:35:46 2026 +0500  Muhammad Anas Naveed  [ffigen] Default compiler options for C++ (dart-lang/native#3645)
  eb6ea1e56  Thu Sep 17 09:28:38 2026 +1000  Liam Appelbe  [ffigen][jnigen] More docs (dart-lang/native#3649)
  da786131c  Thu Sep 17 09:06:20 2026 +1000  Liam Appelbe  [ffigen][jnigen] YAML migration skills (dart-lang/native#3648)
  fc0491997  Wed Sep 16 15:37:19 2026 -0700  Brian Quinlan  [objective_c] don't use autorelease for `toNSDate` (dart-lang/native#3650)
  f7f9a4556  Wed Sep 16 17:32:47 2026 +0200  Daco Harkes  [code_assets] [hooks_runner] [native_toolchain_c] Prepare for release (dart-lang/native#3642)
  1c60c437c  Wed Sep 16 13:40:31 2026 +0200  Daco Harkes  [hooks_runner] Restore non-breaking `KernelAssetPath.toJson` and add `toJsonForTarget` (dart-lang/native#3643)
  7667162b3  Wed Sep 16 11:46:18 2026 +0200  Daco Harkes  [infra] Use `dependency_validator` in `tool/ci.dart` (dart-lang/native#3646)
  f6d153d01  Tue Sep 15 19:32:08 2026 -0700  Brian Quinlan  [objective_c] Fix potential leaks in converts (dart-lang/native#3647)
  cb2c62331  Wed Sep 16 11:32:42 2026 +1000  Liam Appelbe  [ffigen] Remove YAML from readmes (dart-lang/native#3633)
  22e835728  Wed Sep 16 09:49:02 2026 +1000  Liam Appelbe  [jnigen] Remove yaml from readme (dart-lang/native#3634)
  eb444eee2  Wed Sep 16 09:48:04 2026 +1000  Liam Appelbe  [infra] Add and fix `unawaited_futures` and `discarded_futures` lints (dart-lang/native#3639)
  0f419f0d2  Wed Sep 16 09:47:44 2026 +1000  Liam Appelbe  [infra] Switch from coveralls to codecov (dart-lang/native#3626)

shelf (https://github.com/dart-lang/shelf/compare/f36dd68..e5c8dc6):
  e5c8dc6  Tue Sep 15 18:15:41 2026 -0700  Kevin Moore  fix(shelf_static): ignore suffix ranges selecting zero bytes (dart-lang/shelf#541)

test (https://github.com/dart-lang/test/compare/c80d53d..9946c95):
  9946c955  Mon Sep 21 12:31:54 2026 -0700  Nate Bosch  Fix a race in the frontend server client fake (dart-lang/test#2762)
  48c3fdf6  Fri Sep 18 18:52:52 2026 -0700  Nate Bosch  Fix race conditions during test load (dart-lang/test#2761)
  5d74864b  Fri Sep 18 16:25:57 2026 -0700  Nate Bosch  Remove mentions of Travis (dart-lang/test#2760)
  5c4d9b25  Fri Sep 18 12:49:00 2026 -0700  Nate Bosch  Use consistent *Checks naming for prints (dart-lang/test#2759)
  f927df26  Fri Sep 18 12:15:49 2026 -0700  Kevin Moore  feat(checks): add prints expectations (`#2742`) (dart-lang/test#2743)
  347a5af2  Fri Sep 18 12:09:15 2026 -0700  Nate Bosch  Add an example for every matcher (dart-lang/test#2757)
  6358dbb3  Thu Sep 17 15:10:08 2026 -0700  Nate Bosch  Add an example for every checks expectation, and fix the bugs they exposed (dart-lang/test#2756)
  88202adc  Thu Sep 17 14:13:30 2026 +0200  Sigurd Meldgaard  New flag --shard-by-suite

tools (https://github.com/dart-lang/tools/compare/1b0c3bb..3614ce0):
  3614ce06  Fri Sep 18 10:07:20 2026 -0700  Kevin Moore  chore(unified_analytics): remove dart:mirrors usage in test/event_test.dart (dart-lang/tools#2602)
  7550ce13  Fri Sep 18 07:56:44 2026 -0700  Kevin Moore  chore(markdown): remove dart:mirrors usage in tool/stats_lib.dart (dart-lang/tools#2600)

[email protected]

Change-Id: Ide262779269adab780d314d80c9f82b97a79391f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/552741
Commit-Queue: Nate Bosch <[email protected]>
Reviewed-by: Brian Quinlan <[email protected]>
@kevmoo kevmoo mentioned this pull request Sep 23, 2026
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package:checks: Add prints expectation for checking captured output

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