Background Jobs (Bootstrap + Stage 1-2) by UdeshyaDhungana · Pull Request #230 · codecrafters-io/shell-tester

UdeshyaDhungana · 2026-02-24T05:50:43Z

Note

Medium Risk
Adds new stage slugs and assertion logic around background process output formatting, which could introduce flakiness across different shells/PTY behavior; otherwise changes are isolated to the tester and fixtures.

Overview
Adds a new Background Jobs extension with Stage af3 and at7, including new stage handlers (testBG1/testBG2) and test-case helpers to validate jobs being registered as a builtin, jobs output (including empty output), and background launches via cmd & emitting "[job] PID" and returning to the prompt.

Wires the new stages into the tester definition, Makefile test targets (including test_background_jobs_w_bash), and course metadata, and expands fixtures/scenarios to cover common failure modes (bad output format/job number) plus output normalization for variable job/PID values. Updates local docker test runner modes (adds tests_excluding_ash, allows default test with ash) and refactors BuildColoredErrorMessage parameter naming/usage; go.mod/go.sum pick up go-humanize indirectly.

^{Written by Cursor Bugbot for commit 7356938. This will update automatically on new commits. Configure here.}

…estCase and JobsBuiltinTestCase

…ition; record fixtures

internal/stages_test.go

Makefile

internal/stages_test.go

Makefile

internal/test_cases/background_command_response_test_case.go

…ponseTestCase The second AssertWithPrompt() call on line 67 was redundant because: - No new assertions were added after the first call on line 43 - No commands were sent to change the screen state - Assertions are not cleared after execution - This deviated from the pattern used in all other test cases

…d-test-assertion-7037 Background command test assertion

internal/test_cases/jobs_builtin_response_test_case.go

rohitpaulk · 2026-02-24T22:13:20Z

internal/test_cases/background_command_response_test_case.go

+	jobNumberRegexp := regexp.MustCompile(`\[(\d+)\]\s+(\d+)`)
+	matches := jobNumberRegexp.FindStringSubmatch(outputText)
+
+	if len(matches) != 3 {


@UdeshyaDhungana what happens when the user prints an incorrect line (that doesn't match the regex?), I don't see that handled here. Also, we should probably verify the PID? That could be incorrect too.

Added failure cases and updated test case to deliver correct error message.

rohitpaulk · 2026-02-24T22:18:37Z

internal/test_cases/background_command_response_test_case.go

+	outputLine := asserter.Shell.GetScreenState().GetRow(asserter.GetLastLoggedRowIndex())
+	outputText := outputLine.String()
+
+	// Keeping the capture group for PGID as well: we might need it later


@UdeshyaDhungana is this needed for now? It makes our assertions a bit less strict, unless it's a valid case for our current tests I'd remove

I removed the PGID capture group. We won't need it for this extension.

rohitpaulk · 2026-02-24T22:21:33Z

internal/test_cases/jobs_builtin_response_test_case.go

+		}
+
+		// TODO: Remove after PR review: The regex here complies with the Bash's implementation of 'jobs'
+		// Should I add the pattern compatible with ZSH's output as well?


Depends, what are the the differences @UdeshyaDhungana?

@rohitpaulk Here is a short comparison:

ZSH:

[1] running sleep 20 [2] - running sleep 300 [3] + running sleep 40

Bash

[1] Running sleep 200 & [2]- Running sleep 400 & [3]+ Running sleep 500 &

Differences:

ZSH uses a space separator between job number and marker (+/-)

ZSH uses lowercase for job status (eg. running, done)

Bash always shows an & symbol for running jobs, zsh drops it

I've changed the regex to match both of these shell's outputs.

Yep, sounds good! I think it's worth allowing both

rohitpaulk · 2026-02-24T22:24:40Z

internal/test_cases/jobs_builtin_response_test_case.go

+		)
+
+		allLinesAssertions = append(allLinesAssertions, assertions.SingleLineAssertion{
+			FallbackPatterns: []*regexp.Regexp{regex},


If we have assertions without expectedOutput, not sure how the error message is going to look like. We don't expose regexes to users afaik, so I imagine this'd be confusing.

@UdeshyaDhungana let's add test cases for failures - I think these are pretty basic mistakes that we'd have caught if we explicitly thought about what happens when users make mistakes

Added regex mismatch error messages with hints pointing to regex101 just like we do in grep tester.

…e cases; Make JobsBuiltinResponseTestCase to support both bash and zsh patterns

…orMessageForExpectedOutputMismatch

…bs_incorrect_output_format

…at fixtures

internal/utils/utils.go

internal/assertions/single_line_assertion.go

internal/test_cases/jobs_builtin_response_test_case.go

internal/test_helpers/fixtures/background_jobs_incorrect_output_format

…ter logs

internal/test_cases/jobs_builtin_response_test_case.go

Changed (\s)? to \s* in the jobs builtin regex pattern to handle ZSH's labeled job format which uses 2+ spaces before the +/- marker (e.g., '[2] - running' instead of '[2]- running').

…rmat-1863 Jobs regex ZSH format

internal/assertions/single_line_regex_assertion.go

cursor · 2026-02-25T12:06:15Z

Bugbot Autofix prepared fixes for 1 of the 1 bugs found in the latest run.

✅ Fixed: Inspect returns wrong type name for regex assertion
- Changed the format string in Inspect() from "SingleLineAssertion" to "SingleLineRegexAssertion" to correctly identify the assertion type.

Or push these changes by commenting:

@cursor push 3c7ad29063

Preview (3c7ad29063)

diff --git a/internal/assertions/single_line_regex_assertion.go b/internal/assertions/single_line_regex_assertion.go
--- a/internal/assertions/single_line_regex_assertion.go
+++ b/internal/assertions/single_line_regex_assertion.go
@@ -27,7 +27,7 @@
 		patterns = append(patterns, pattern.String())
 	}
 
-	return fmt.Sprintf("SingleLineAssertion (%q)", strings.Join(patterns, "\n"))
+	return fmt.Sprintf("SingleLineRegexAssertion (%q)", strings.Join(patterns, "\n"))
 }
 
 func (a SingleLineRegexAssertion) Run(screenState screen_state.ScreenState, startRowIndex int) (processedRowCount int, err *AssertionError) {

…nspect-name-eaf1 Regex assertion inspect name

UdeshyaDhungana · 2026-02-25T12:39:12Z

Added failure cases
Added a SingleLineRegexAssertion instead of re-using SingleLineAssertion: There were a lot of if block checks so decided to separate it into a different test case

rohitpaulk · 2026-02-26T01:37:11Z

internal/test_helpers/fixtures/background_jobs_incorrect_output_format

+[33m[tester::#AT7] [0m[91m^ Line does not match the expected regex.[0m
+[33m[tester::#AT7] [0m[91m[31mReceived:[0m "[1]2551"[0m
+[33m[tester::#AT7] [0m[91m[32mExpected line to match the following regex:[0m
+[33m[tester::#AT7] [0m[91m[0m[32m\[\d+\]\s+\d+(Hint: https://regex101.com/?regex=%5C%5B%5Cd%2B%5C%5D%5Cs%2B%5Cd%2B&testString=%5B1%5D2551)[0m[0m


@UdeshyaDhungana I think this is going to be super confusing. Can we try just setting expected output to "[1] "?

Expected: "[1] <PID>" Received: "[1]2551"

Let's not expose the regex.

rohitpaulk · 2026-02-26T01:38:43Z

internal/test_helpers/fixtures/background_jobs_incorrect_job_number

+[33m[tester::#AT7] [0m[94mRunning ./your_program.sh[0m
+[33m[your-program] [0m[0m$ sleep 100 &[0m
+[33m[your-program] [0m[0m[0] 2652[0m
+[33m[tester::#AT7] [0m[91mExpected job number to be 1, got 0[0m


Wonder if this could just use our existing format?

Expected: "[1] <PID>" Received: "[0] 2652"

Might not be super obvious what job number is here, and I think our assertion could in fact be simpler and re-use the existing ones if we do this?

rohitpaulk · 2026-02-26T01:39:29Z

internal/assertions/single_line_regex_assertion.go

+	return 0, &AssertionError{
+		ErrorRowIndex: startRowIndex,
+		Message: fmt.Sprintf("Line does not match %s.\n%s",
+			english.PluralWord(len(a.ExpectedRegexPatterns), "the expected regex", "any of the expected regexes"),


Let's scrap this - we shouldn't expose regex to users, can be confusing. We should keep our expectations very human-level, just seeing the expected vs. received output should make it clear what's wrong and needs to be fixed

cursor

Cursor Bugbot has reviewed your changes and found 1 potential issue.

Bugbot Autofix prepared a fix for the issue found in the latest run.

✅ Fixed: Unescaped regex metacharacter in job marker causes panic
- Wrapped the marker variable with regexp.QuoteMeta() to escape the '+' character that would cause an invalid regex pattern when CurrentJob is used.

Or push these changes by commenting:

@cursor push a79e15ad0f

Preview (a79e15ad0f)

diff --git a/internal/test_cases/jobs_builtin_response_test_case.go b/internal/test_cases/jobs_builtin_response_test_case.go
--- a/internal/test_cases/jobs_builtin_response_test_case.go
+++ b/internal/test_cases/jobs_builtin_response_test_case.go
@@ -61,7 +61,7 @@
 		regexString := fmt.Sprintf(
 			`^\[%d\]\s*%s\s+(?i)%s\s+(?-i)%s`,
 			outputEntry.JobNumber,
-			marker,
+			regexp.QuoteMeta(marker),
 			regexp.QuoteMeta(outputEntry.Status),
 			regexp.QuoteMeta(outputEntry.LaunchCommand),
 		)

cursor · 2026-02-26T04:36:44Z

internal/test_cases/jobs_builtin_response_test_case.go

+		regexString := fmt.Sprintf(
+			`^\[%d\]\s*%s\s+(?i)%s\s+(?-i)%s`,
+			outputEntry.JobNumber,
+			marker,


Unescaped regex metacharacter in job marker causes panic

High Severity

The marker value from convertJobMarkerToString is interpolated directly into the regex pattern on line 62 without regexp.QuoteMeta(). When CurrentJob is used, marker is "+", producing the pattern \s*+ in the regex string. Go's RE2 engine does not support possessive quantifiers, so regexp.MustCompile on line 77 will panic at runtime. The Status and LaunchCommand fields are properly escaped but marker is not.

Additional Locations (1)

internal/test_cases/jobs_builtin_response_test_case.go#L112-L114

Please ignore this. I've changed this in the next PR where this is actually used, including error cases.

rohitpaulk

Looks good but we should add in the PID check too (can be another PR)

rohitpaulk · 2026-02-26T04:49:57Z

internal/test_helpers/fixtures/background_jobs_incorrect_job_number

+[33m[your-program] [0m[0m[0] 2233[0m
+[33m[tester::#AT7] [0m[91m^ Line does not match expected value.[0m
+[33m[tester::#AT7] [0m[91m[32mExpected:[0m "[1] <PID>"[0m
+[33m[tester::#AT7] [0m[91m[31mReceived:[0m "[0] 2233"[0m


@UdeshyaDhungana another test we should add: invalid PID. A user could print 1234 for the PID and pass at the moment

Sure. Will raise a new PR.

UdeshyaDhungana added 3 commits February 24, 2026 09:23

Add stages 1-4 for background jobs; Design BackgroundCommandResponseT…

1171636

…estCase and JobsBuiltinTestCase

Add comment regarding regex pattern in jobs builtin test case

0a3da82

Remove stages 3 and 4; add stages in stages_test; update course defin…

26c0ecf

…ition; record fixtures

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UdeshyaDhungana added 2 commits February 24, 2026 11:44

Trim down stages 3 and 4 leftovers

72ea40b

Remove trailing comman in JSON definiton of background stages

75208c4

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UdeshyaDhungana added 3 commits February 24, 2026 11:52

Update fixtures normalizer regex

6249387

Revert accidental extra space in Makefile

1d69709

Remove unused struct method in background command response test case

7d1f65e

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Apply cursor suggestion and typo fixes

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UdeshyaDhungana added 2 commits February 24, 2026 14:46

Merge pull request #233 from codecrafters-io/cursor/background-comman…

e0155e0

…d-test-assertion-7037 Background command test assertion

Make small typo fixes and changes to the PR

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UdeshyaDhungana requested a review from rohitpaulk February 24, 2026 10:38

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UdeshyaDhungana added 8 commits February 25, 2026 12:59

Add case for regex mismatch when expected output is empty; Add failur…

55d8e89

…e cases; Make JobsBuiltinResponseTestCase to support both bash and zsh patterns

Merge branch 'main' to bg-jobs

87d1a00

Revert zsh/your_shell.sh

dce2cc2

Rename BuildColoredErrorMessageForUnexpectedOutput to BuildColoredErr…

8083f3a

…orMessageForExpectedOutputMismatch

Update normalizerTesterOutput function to add regex for background_jo…

b33956f

…bs_incorrect_output_format

Fix: bug in normalizeTesterOutput

e302125

Update normalizeTesterOutput

8c2ba37

Add third regex for normalizing background_jobs_incorrect_output_form…

2456c22

…at fixtures

Fix typos and bugs; update docker script

06d9792

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Fix empty expected output case in single line assertion

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Use SingleLineRegexAssertion in Background Jobs stages

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Update SingleLineRegexAssertion and JobsBuiltinRegexAssertion for bet…

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…ter logs

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Fix ZSH labeled job regex to allow multiple spaces before marker

d874c0e

Changed (\s)? to \s* in the jobs builtin regex pattern to handle ZSH's labeled job format which uses 2+ spaces before the +/- marker (e.g., '[2] - running' instead of '[2]- running').

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Merge pull request #255 from codecrafters-io/cursor/jobs-regex-zsh-fo…

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…rmat-1863 Jobs regex ZSH format

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Fix Inspect() to return correct type name for SingleLineRegexAssertion

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Merge pull request #257 from codecrafters-io/cursor/regex-assertion-i…

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…nspect-name-eaf1 Regex assertion inspect name

UdeshyaDhungana requested a review from rohitpaulk February 25, 2026 12:38

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UdeshyaDhungana added 5 commits February 26, 2026 09:55

Re-use SingleLineAssertion in BackgroundCommandResponseTestCase

aeabc7d

Revert back single_line_assertion.go

ea484a2

Use ExpectedOutput in JobsBuiltinResponseTestCase

4416596

Record fixtures

54d0cfc

Modify normalizer fixtures in stages_test

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UdeshyaDhungana requested a review from rohitpaulk February 26, 2026 04:44

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Unescaped regex metacharacter in job marker causes panic

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