Add --fail-under flag for minimum coverage threshold

[vvs-personalstash]

Implement --fail-under Flag for Enforcing Minimum Code Coverage Thresholds

This pull request introduces a new command-line flag, --fail-under, to the package:coverage tool. The feature is modeled after the behavior of the --fail-under flag in Python’s coverage.py library.

Overview of Changes

New Feature: --fail-under

• Accepts a numeric percentage value representing the minimum acceptable code coverage.
• If the actual test coverage falls below this threshold, the tool will return a non-zero exit code (exit(1)), signaling failure.

Optional Precision Control: --precision

• An additional --precision flag has been introduced to control the number of decimal places shown in the computed coverage percentage.

Need Clarity

-Currently i have only added tests for directly testing the coverage percentage calculator,Is it sufficient or should I modify the test_with_coverage_test to test the flag also

• I’ve reviewed the contributor guide and applied the relevant portions to this PR.

Fixes #514

[liamappelbe]

The unit test that checks the calculateCoveragePercentage function is a good start, but we'll also need an integration test to verify that the check's logic works: one test that verifies that the command succeeds when the coverage percentage is above the threshold, and test that verifies it fails when the coverage is below the threshold. There's a few existing integration tests that you can piggy back on. Maybe test_with_coverage_test.dart, but there's others too.

[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:bazel_worker	1.1.3	already published at pub.dev
package:benchmark_harness	2.3.1	already published at pub.dev
package:boolean_selector	2.1.2	already published at pub.dev
package:browser_launcher	1.1.3	already published at pub.dev
package:cli_config	0.2.1-wip	WIP (no publish necessary)
package:cli_util	0.4.2	already published at pub.dev
package:clock	1.1.2	already published at pub.dev
package:code_builder	4.10.2-wip	WIP (no publish necessary)
package:coverage	1.13.0-wip	WIP (no publish necessary)
package:csslib	1.0.2	already published at pub.dev
package:extension_discovery	2.1.0	already published at pub.dev
package:file	7.0.2-wip	WIP (no publish necessary)
package:file_testing	3.1.0-wip	WIP (no publish necessary)
package:glob	2.1.3	already published at pub.dev
package:graphs	2.3.3-wip	WIP (no publish necessary)
package:html	0.15.6	already published at pub.dev
package:io	1.1.0-wip	WIP (no publish necessary)
package:json_rpc_2	4.0.0	ready to publish	json_rpc_2-v4.0.0
package:markdown	7.3.1-wip	WIP (no publish necessary)
package:mime	2.0.0	already published at pub.dev
package:oauth2	2.0.4-wip	WIP (no publish necessary)
package:package_config	2.3.0-wip	WIP (no publish necessary)
package:pool	1.5.2-wip	WIP (no publish necessary)
package:pub_semver	2.2.0	already published at pub.dev
package:pubspec_parse	1.5.0	already published at pub.dev
package:source_map_stack_trace	2.1.3-wip	WIP (no publish necessary)
package:source_maps	0.10.14-wip	WIP (no publish necessary)
package:source_span	1.10.1	already published at pub.dev
package:sse	4.1.8	ready to publish	sse-v4.1.8
package:stack_trace	1.12.1	already published at pub.dev
package:stream_channel	2.1.4	already published at pub.dev
package:stream_transform	2.1.2-wip	WIP (no publish necessary)
package:string_scanner	1.4.1	already published at pub.dev
package:term_glyph	1.2.3-wip	WIP (no publish necessary)
package:test_reflective_loader	0.2.3	already published at pub.dev
package:timing	1.0.2	already published at pub.dev
package:unified_analytics	8.0.1	already published at pub.dev
package:watcher	1.1.1	already published at pub.dev
package:yaml	3.1.3	already published at pub.dev
package:yaml_edit	2.2.2	already published at pub.dev

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

[github-actions]

PR Health

Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
coverage	None	1.12.0	1.13.0-wip	1.12.0	✔️

Changelog Entry ✔️

Package	Changed Files

Changes to files need to be accounted for in their respective changelogs.

Coverage ⚠️

File	Coverage
pkgs/coverage/bin/format_coverage.dart	💔 44 % ⬇️ 9 %
pkgs/coverage/bin/test_with_coverage.dart	💚 37 % ⬆️ 2 %
pkgs/coverage/lib/src/coverage_percentage.dart	💚 100 %

This check for test coverage is informational (issues shown here will not fail the PR).

This check can be disabled by tagging the PR with skip-coverage-check.

API leaks ✔️

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

Package	Leaked API symbols

License Headers ✔️

// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

Files
no missing headers

All source files should start with a license header.

Unrelated files missing license headers

Files
pkgs/bazel_worker/benchmark/benchmark.dart
pkgs/bazel_worker/example/client.dart
pkgs/bazel_worker/example/worker.dart
pkgs/benchmark_harness/integration_test/perf_benchmark_test.dart
pkgs/boolean_selector/example/example.dart
pkgs/clock/lib/clock.dart
pkgs/clock/lib/src/clock.dart
pkgs/clock/lib/src/default.dart
pkgs/clock/lib/src/stopwatch.dart
pkgs/clock/lib/src/utils.dart
pkgs/clock/test/clock_test.dart
pkgs/clock/test/default_test.dart
pkgs/clock/test/stopwatch_test.dart
pkgs/clock/test/utils.dart
pkgs/coverage/lib/src/coverage_options.dart
pkgs/coverage/test/collect_coverage_config_test.dart
pkgs/coverage/test/config_file_locator_test.dart
pkgs/html/example/main.dart
pkgs/html/lib/dom.dart
pkgs/html/lib/dom_parsing.dart
pkgs/html/lib/html_escape.dart
pkgs/html/lib/parser.dart
pkgs/html/lib/src/constants.dart
pkgs/html/lib/src/encoding_parser.dart
pkgs/html/lib/src/html_input_stream.dart
pkgs/html/lib/src/list_proxy.dart
pkgs/html/lib/src/query_selector.dart
pkgs/html/lib/src/token.dart
pkgs/html/lib/src/tokenizer.dart
pkgs/html/lib/src/treebuilder.dart
pkgs/html/lib/src/utils.dart
pkgs/html/test/dom_test.dart
pkgs/html/test/parser_feature_test.dart
pkgs/html/test/parser_test.dart
pkgs/html/test/query_selector_test.dart
pkgs/html/test/selectors/level1_baseline_test.dart
pkgs/html/test/selectors/level1_lib.dart
pkgs/html/test/selectors/selectors.dart
pkgs/html/test/support.dart
pkgs/html/test/tokenizer_test.dart
pkgs/html/test/trie_test.dart
pkgs/html/tool/generate_trie.dart
pkgs/pubspec_parse/test/git_uri_test.dart
pkgs/stack_trace/example/example.dart
pkgs/watcher/test/custom_watcher_factory_test.dart
pkgs/yaml_edit/example/example.dart

[coveralls]

Pull Request Test Coverage Report for Build 14722503205

Details

• 11 of 11 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 93.562%

---

Totals
Change from base Build 14686572841:	0.1%
Covered Lines:	683
Relevant Lines:	730

---

💛 - Coveralls

[vvs-personalstash]

The unit test that checks the calculateCoveragePercentage function is a good start, but we'll also need an integration test to verify that the check's logic works: one test that verifies that the command succeeds when the coverage percentage is above the threshold, and test that verifies it fails when the coverage is below the threshold. There's a few existing integration tests that you can piggy back on. Maybe test_with_coverage_test.dart, but there's others too.

Hi Liam I decided to use the test_with_coverage_test to create the integration tests both checking whether the command passes when threshold is met and exits with exit(1) if not and also modified the test_with_coverage_package to test for branch hits also.I would like to know if these tests work for you or do you have a different approach in mind and if I am making any mistakes in my implementations till now.
Also I have my Majors this week so I might take some time to make changes.Thank You.

[liamappelbe]

Looking good. Just a couple more tiny comments, then I think this will be ready to land.

[liamappelbe]

Oh, also take a look at the analyzer failures on the GitHub bot