mbj/mutant

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Mutation testing for Ruby. AI writes your code. AI writes your tests. But who tests the tests?

Stars: 2.2k
Forks: 162
Open beginner issues: 0
Indexed issues: 116
Avg merge: 4d 18h
Merged PRs (30d): 7

Dominant language: Ruby
License: No license data
Last GitHub push: Sep 17, 2026
Latest indexed: Sep 20, 2026
Contributing guide: Contributing guide
Code of conduct: No code of conduct
Beginner labels: No beginner labels indexed

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116 open issues indexed

Feature request: Support `ignore_patterns` on children of nodes with variable elements Open

Difficulty 3/5 1-2 days Newbie friendliness 48/100

mbj/mutant#1606 · Opened Apr 10, 2026
Add back `@foo` -> `foo` when `attr_reader :foo` or `attr_writer :foo` is defined on the instance Open

Difficulty 5/5 Over a week Newbie friendliness 25/100

mbj/mutant#1592 · 2 comments · Opened Mar 18, 2026
feat: todo file Open

incremental

Difficulty 5/5 Over a week Newbie friendliness 35/100

mbj/mutant#1435 · 3 comments · Opened Apr 3, 2024
Allow `mutant:disable` to apply to inline macros and visibility modifiers Open

Difficulty 3/5 1-2 days Newbie friendliness 35/100

mbj/mutant#1399 · 1 comment · Opened Aug 3, 2023
Add mechanism to hooks to report "true" source location Open

Difficulty 5/5 Over a week Newbie friendliness 25/100

mbj/mutant#1397 · Opened Aug 3, 2023
Failing subjects summary Open

Difficulty 4/5 3-5 days Newbie friendliness 35/100

mbj/mutant#1393 · Opened Jul 14, 2023
Add `--debug-worker` flag to make debugging workers easier Open

enhancement

Difficulty 3/5 1-2 days Newbie friendliness 48/100

mbj/mutant#1388 · 2 comments · Opened Jun 6, 2023
`--since` flag fails when git is configured with a different diff tool Open

Difficulty 4/5 3-5 days Newbie friendliness 35/100

mbj/mutant#1387 · 4 comments · Opened May 22, 2023
SQL mutations Open

mutation

Difficulty 5/5 Over a week Newbie friendliness 25/100

mbj/mutant#1360 · 1 comment · Opened Dec 15, 2022
Choose subjects based on an AST diff when using `--since` Open

enhancement

Difficulty 5/5 Over a week Newbie friendliness 30/100

mbj/mutant#1337 · 2 comments · 1 reaction · Opened Jun 17, 2022
Mutation idea: `foo.all? { |bar| bar == baz }` -> `foo.all?(baz)` Open

mutation

Difficulty 4/5 3-5 days Newbie friendliness 20/100

mbj/mutant#1336 · 1 comment · Opened Jun 14, 2022
Idea: neutral mutation only mode Open

enhancement

Difficulty 5/5 Over a week Newbie friendliness 20/100

mbj/mutant#1334 · 2 comments · Opened May 26, 2022
Expand corpus tests Open

enhancement

Difficulty 3/5 1-2 days Newbie friendliness 45/100

mbj/mutant#1330 · Opened May 2, 2022
Enhance corpus tests Open

enhancement

Difficulty 3/5 1-2 days Newbie friendliness 45/100

mbj/mutant#1329 · Opened May 2, 2022
Improve error UX? Open

Difficulty 4/5 3-5 days Newbie friendliness 25/100

mbj/mutant#1318 · 1 comment · Opened Apr 14, 2022
Skip mutation of `else T.absurd` Open

Difficulty 3/5 1-2 days Newbie friendliness 42/100

mbj/mutant#1289 · 1 comment · Opened Dec 6, 2021
Mutate `str.tr_s(pattern, '')` → `str.delete(pattern)` Open

enhancement mutation

mbj/mutant#1286 · 1 reaction · 1 assignee · Opened Nov 17, 2021
Add numblock specific body mutations Open

enhancement mutation

Difficulty 4/5 3-5 days Newbie friendliness 35/100

mbj/mutant#1256 · Opened Aug 30, 2021
Mutant failures caused by timeouts need to be more prominent Open

enhancement

Difficulty 3/5 1-2 days Newbie friendliness 35/100

mbj/mutant#1251 · Opened Aug 27, 2021
Add mutation from `Array#one?` to `array.length.equal?(1)`. Open

mutation

mbj/mutant#1246 · 1 assignee · Opened Jul 29, 2021
Add mutation of #map to #to_set Open

mutation

Difficulty 3/5 1-2 days Newbie friendliness 35/100

mbj/mutant#1241 · Opened Jul 21, 2021
Fix crash on unexpected method-signature in rspec describe Open

bug

mbj/mutant#1239 · 1 assignee · Opened Jun 11, 2021
Add mutation to ensure stronger persistence method is used Open

enhancement mutation rails

Difficulty 3/5 1-2 days Newbie friendliness 42/100

mbj/mutant#1238 · Opened Jun 11, 2021
Fix crash on extracting subject associations on rspec tests without description Open

Difficulty 3/5 1-2 days Newbie friendliness 30/100

mbj/mutant#1236 · Opened May 31, 2021
Add mutation from `ensure` to `tap` Open

mutation

mbj/mutant#1232 · 1 reaction · 1 assignee · Opened Apr 30, 2021
Feature request: output alive test selectors at end of output Open

enhancement

Difficulty 4/5 3-5 days Newbie friendliness 35/100

mbj/mutant#1208 · 6 comments · 3 reactions · Opened Jan 15, 2021
Change to not execute mutations without a selected tests. Open

Difficulty 4/5 3-5 days Newbie friendliness 20/100

mbj/mutant#1203 · Opened Jan 4, 2021
Add an ability to specify path to the configuration file Open

Difficulty 3/5 1-2 days Newbie friendliness 35/100

mbj/mutant#1171 · 8 comments · 1 reaction · Opened Dec 22, 2020
The `--start-subject` flag does not work as expected with an exact subject Open

bug

Difficulty 3/5 1-2 days Newbie friendliness 45/100

mbj/mutant#1163 · Opened Dec 16, 2020
Add the ability to use as an `rspec` runner Open

enhancement minitest rspec

Difficulty 5/5 Over a week Newbie friendliness 25/100

mbj/mutant#1162 · 2 comments · 1 reaction · Opened Dec 16, 2020
Do not mutate method parameter names when `super` (zsuper) is used Open

mutation

Difficulty 3/5 1-2 days Newbie friendliness 35/100

mbj/mutant#1144 · 4 comments · Opened Dec 8, 2020
Abort on empty subject selection (when not using `--since`) Open

enhancement

Difficulty 3/5 1-2 days Newbie friendliness 25/100

mbj/mutant#1143 · 1 comment · Opened Dec 8, 2020
Verify mutation removing arguments on multi kwargs is present and operational Open

Difficulty 3/5 1-2 days Newbie friendliness 35/100

mbj/mutant#1119 · Opened Nov 22, 2020
Add `insertion_warning` coverage condition Open

Difficulty 3/5 1-2 days Newbie friendliness 25/100

mbj/mutant#1114 · 1 comment · Opened Nov 21, 2020
Add `runtime_warning` coverage condition Open

Difficulty 4/5 3-5 days Newbie friendliness 25/100

mbj/mutant#1113 · 1 comment · Opened Nov 21, 2020
Add `--no-fail-fast` flag Open

enhancement

Difficulty 3/5 1-2 days Newbie friendliness 35/100

mbj/mutant#1110 · Opened Nov 16, 2020
Handle exceptions during mutation generation gracefully Open

Difficulty 4/5 3-5 days Newbie friendliness 35/100

mbj/mutant#1105 · Opened Nov 15, 2020
Document new contributor process Open

documentation

Difficulty 3/5 1-2 days Newbie friendliness 42/100

mbj/mutant#1101 · Opened Nov 12, 2020
Add additional documentation about --start-subject behavior Open

documentation

Difficulty 2/5 1-3 hours Newbie friendliness 38/100

mbj/mutant#1100 · Opened Nov 12, 2020
Handle execution of mutant outside git repository gracefully Open

Difficulty 3/5 1-2 days Newbie friendliness 20/100

mbj/mutant#1083 · Opened Nov 2, 2020
Handle absence of `git` command gracefully Open

Difficulty 3/5 1-2 days Newbie friendliness 25/100

mbj/mutant#1082 · Opened Nov 2, 2020
Provide better error message when `--since` cannot find the reference Open

mbj/mutant#1011 · 1 assignee · Opened Aug 2, 2020
Add --skip-subject and --pending-subject flags Open

enhancement

mbj/mutant#971 · 1 comment · 1 reaction · 1 assignee · Opened Sep 19, 2019
Bug in --since integration causes removed code lines to be used for subject selection Open

bug

mbj/mutant#966 · 1 assignee · Opened Jun 24, 2019
Improve incremental documentation for latest findings on branch references Open

mbj/mutant#947 · 1 assignee · Opened Apr 9, 2019
Print alive mutations while the tool is still running Open

enhancement

Difficulty 4/5 3-5 days Newbie friendliness 35/100

mbj/mutant#946 · Opened Apr 2, 2019
Ruby version target Open

mbj/mutant#841 · 6 comments · 1 assignee · Opened Jan 5, 2019
Allow to configure integration specific requires. Open

enhancement

mbj/mutant#783 · 1 assignee · Opened Nov 28, 2018
Add mutation that removes a double splat from expressions Open

mutation

Difficulty 3/5 1-2 days Newbie friendliness 45/100

mbj/mutant#763 · Opened Nov 16, 2018
Rails with multiple test databases Open

question

mbj/mutant#757 · 1 comment · 1 assignee · Opened Nov 11, 2018

mbj/mutant

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