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Improve test coverage for $ARGUMENTS by mining reference test suites from yash, GNU coreutils, and uutils/coreutils for gaps in our scenario tests.

⛔ STOP — READ THIS BEFORE DOING ANYTHING ELSE ⛔

You MUST follow this execution protocol. Skipping steps causes missed coverage gaps or broken tests.

IMPORTANT: Never ask the user questions or wait for confirmation. Always process ALL targets autonomously from start to finish.

1. Create the full task list FIRST

Your very first action — before reading ANY files, before writing ANY code — is to create the task list. Call TaskCreate for each step:

1. "Step 1: Enumerate all targets"
2. "Step 2: Download reference test suites"

Then for each target discovered in Step 1, you will dynamically create tasks for Steps 3–11 (see "Per-target loop" below).

2. Execution order

The workflow has two phases:

Phase A — Setup (once): Step 1 → Step 2

Phase B — Per-target loop: Process targets ONE AT A TIME, in sequence. For each target, run Steps 3 → 4 → 5 → 6 → 7 → 8 → 9 → 10 sequentially. Complete ALL steps for one target before starting the next. Do NOT process multiple targets in parallel.

Before starting step N, call TaskList and verify step N-1 is completed. Set step N to in_progress.

Before marking any step as completed:

• Re-read the step description and verify every sub-bullet is satisfied
• If any sub-bullet is not done, keep working — do NOT mark it completed

Context

The safe shell interpreter (interp/) implements all commands as Go builtins — it never executes host binaries. Test scenarios are YAML files in tests/scenarios/ that are automatically validated against both the shell and bash (via Docker).

Reference test suites

Three external test suites serve as coverage references:

1. yash — a POSIX-compliant shell with thorough tests for shell language features (control flow, expansion, quoting, redirections, etc.)

   • Repository: https://github.com/magicant/yash/tree/trunk/tests
   • License: GPL v2; use for test design reference only, not verbatim copy
   • Strengths: POSIX shell language edge cases, quoting, expansion, control flow

2. GNU coreutils — reference implementation tests for command-line utilities

   • Repository: https://github.com/coreutils/coreutils/tree/master/tests
   • License: GPL v3; use for test design reference only
   • Offline: resources/gnu-coreutils-tests/
   • Strengths: flag combinations, edge cases, error handling, multi-file behavior

3. uutils/coreutils — Rust rewrite of coreutils with MIT-licensed tests

   • Repository: https://github.com/uutils/coreutils/tree/main/tests
   • License: MIT; test logic can be freely adapted
   • Offline: resources/uutils-tests/
   • Strengths: integer edge cases, Unicode, binary input, overflow guards, cross-platform

How to decide which suite to consult

Phase A — Setup

Step 1: Enumerate all targets

Based on the argument ($ARGUMENTS), build the ordered list of targets to process:

• A specific command (e.g. cat, head, grep): The target list is just that one command. Verify it exists as an implemented builtin by checking interp/builtins/.
• A shell feature (e.g. var_expand, globbing, pipe): The target list is just that one feature. Verify the directory exists in tests/scenarios/shell/.
• all: Enumerate every command and shell feature:

# List all implemented builtin commands
ls interp/builtins/ | grep -v _test.go | sed 's/\.go$//' | sort

# List all shell feature test directories
ls tests/scenarios/shell/ | sort

# List all command test directories
ls tests/scenarios/cmd/ | sort

For each target, count its current scenario tests and note the count. Sort targets by test count ascending (fewest tests first) to prioritize the least-covered targets.

Log the full target list as a table (do NOT ask for confirmation — always process all targets):

Then immediately create tasks for the per-target loop. For each target, call TaskCreate for:

• "Step 3: Audit existing coverage — <target>"
• "Step 4: Identify coverage gaps — <target>"
• "Step 5: Write new scenario tests — <target>"
• "Step 6: Check for duplicate tests — <target>"
• "Step 7: Review skip_assert_against_bash flags — <target>"
• "Step 8: Review unnecessary Windows-specific assertions — <target>"
• "Step 9: Fix failing tests — <target>"
• "Step 10: Commit, push, and post report — <target>"

Set up blockedBy dependencies so each target's Step 3 is blocked by the previous target's Step 10 (and by Step 2 for the first target).

Step 2: Download reference test suites

Download all reference suites once, before starting the per-target loop.

For builtin commands

First check if offline resources exist:

ls resources/gnu-coreutils-tests/ 2>/dev/null | head -5
ls resources/uutils-tests/ 2>/dev/null | head -5

If offline resources are available, use them. Otherwise download:

# GNU coreutils tests
curl -sL https://github.com/coreutils/coreutils/archive/refs/heads/master.tar.gz | tar -xz -C /tmp
# Tests are at: /tmp/coreutils-master/tests/<command>/

# uutils tests
curl -sL https://github.com/uutils/coreutils/archive/refs/heads/main.tar.gz | tar -xz -C /tmp
# Tests are at: /tmp/coreutils-main/tests/by-util/test_<command>.rs

For shell features

Download the yash test suite:

curl -sL https://github.com/magicant/yash/archive/refs/heads/trunk.tar.gz | tar -xz -C /tmp
# Tests are at: /tmp/yash-trunk/tests/

Only download the suites needed for the targets in the list. If all targets are commands, skip yash (unless needed for integration patterns). If all targets are shell features, skip GNU/uutils.

Phase B — Per-target loop

For each target in the ordered list from Step 1, execute Steps 3–11 sequentially. Replace <target> below with the current command or shell feature name.

Step 3: Audit existing coverage

Read all existing scenario tests for the current target:

# For a command:
find tests/scenarios/cmd/<target>/ -name "*.yaml" | sort

# For a shell feature:
find tests/scenarios/shell/<target>/ -name "*.yaml" | sort

Read each YAML file and build a coverage matrix. For each test, note:

• What flag/feature/behavior it exercises
• Whether it covers happy path, edge cases, or error cases
• Whether it has skip_assert_against_bash: true

Also read the Go test files if they exist:

# For a command:
find interp/builtins/ -path "*<target>*_test.go" | sort
find interp/ -name "builtin_<target>*_test.go" | sort

Read the relevant reference test files for this specific target (from the suites downloaded in Step 2):

• For commands: read GNU coreutils and uutils test files for <target>, plus skim yash for integration patterns
• For shell features: read the relevant yash test files

Build a summary table of what is currently tested.

Step 4: Identify coverage gaps

Cross-reference the reference test suites against existing coverage (Step 3) to find gaps.

Gap categories to look for

For commands:

For shell features:

Filtering

Skip reference tests that:

• Test flags we intentionally do not implement (check the builtin's doc comment or --help output)
• Test write/execute operations that our sandbox blocks
• Test platform-specific kernel features (/proc, /sys, inotify)
• Test GNU-specific extensions beyond POSIX that we don't support
• Rely on external commands we don't implement

Priority

Rank gaps by importance:

1. P1 — Missing basic coverage: A flag or feature has zero scenario tests
2. P2 — Missing edge cases: Basic behavior is tested but edge cases from reference suites are not
3. P3 — Missing error paths: Error conditions referenced in test suites are not covered
4. P4 — Missing combinations: Flag combinations or integration scenarios are not covered

Log the gap analysis as a summary table (do NOT ask for confirmation — proceed directly to writing tests). Include:

• The gap description
• The priority level
• Whether it needs skip_assert_against_bash: true

Step 5: Write new scenario tests

For each identified gap, create a YAML scenario test file. Follow the project conventions:

File organization

tests/scenarios/cmd/<command>/<category>/<test_name>.yaml
tests/scenarios/shell/<feature>/<category>/<test_name>.yaml

YAML format

description: One sentence describing what this scenario tests.
setup:
  files:
    - path: relative/path/in/tempdir
      content: "file content here"
      chmod: 0644           # optional
      symlink: target/path  # optional
input:
  allowed_paths: ["$DIR"]   # "$DIR" resolves to the temp dir
  script: |+
    command arguments
expect:
  stdout: "expected output\n"
  stderr: ""
  exit_code: 0

Rules

• No source attribution: Do NOT include comments referencing external test suites in YAML test files
• stdout_contains and stderr_contains must be YAML lists, not scalar strings
• Prefer expect.stderr (exact match) over stderr_contains unless the error message is platform-specific
• Prefer expect.stdout (exact match) over stdout_contains whenever possible
• Tests are asserted against bash by default — only set skip_assert_against_bash: true for features that intentionally diverge from bash. When using this flag, always add a YAML comment explaining why (e.g. # skip: sandbox blocks write operations, # skip: intentionally restricts redirections)
• Use stdout_windows/stderr_windows for platform-specific output differences
• Use |+ for multi-line content to preserve trailing newlines
• Do not use echo -n — the echo builtin does not support -n and will emit -n literally. Use printf instead for newline-free output
• When testing error messages from our builtins, the error format is typically <command>: <message> — verify by running the command in the shell first

Determining expected output

For each new test, determine the correct expected output:

Method A — Run in our shell first:

go run . -c '<script>'

Method B — Run in bash (Docker):

docker run --rm debian:bookworm-slim bash -c '<script>'

Method C — Run locally with bash:

bash -c '<script>'

Always verify that our shell output matches bash for tests without skip_assert_against_bash: true.

Batch size

Write tests in batches of 10-15 files, then run verification (Step 9) before writing more. This catches format errors early.

Step 6: Check for duplicate tests

Scan all scenario tests for the target (including newly written ones) and identify duplicates — tests that exercise the same behavior with the same or nearly identical scripts and expected output.

How to detect duplicates

1. Exact duplicates: Two YAML files with identical input.script and expect sections (possibly different descriptions or filenames)
2. Near duplicates: Tests with functionally equivalent scripts that test the same behavior (e.g. same command with same flags, just different variable names or file content that doesn't change the behavior being tested)
3. Subset duplicates: A test that is a strict subset of another test — everything it validates is already covered by a more comprehensive test

Process

# For each pair of YAML files, compare the script and expected output
# Look for files with identical or near-identical scripts
find tests/scenarios/cmd/<target>/ -name "*.yaml" -exec grep -l "script:" {} \; | sort

For each duplicate found:

• Note which files are duplicates and why
• Recommend which one to keep (prefer the one with better description, more complete assertions, or better file organization)
• Remove the duplicate file

If no duplicates are found, note that and move on.

Step 7: Review skip_assert_against_bash flags

Scan all scenario tests for the target that have skip_assert_against_bash: true and evaluate whether the flag is still needed.

grep -rl "skip_assert_against_bash: true" tests/scenarios/cmd/<target>/ 2>/dev/null
grep -rl "skip_assert_against_bash: true" tests/scenarios/shell/<target>/ 2>/dev/null

For each flagged test:

1. Read the test to understand what behavior it tests
2. Determine if the divergence is still intentional: Run the script in bash to see what bash produces

   bash -c '<script from test>'
   # or
   docker run --rm debian:bookworm-slim bash -c '<script>'

3. Classify the result:

For each test where the flag is removed, verify it passes against bash:

RSHELL_BASH_TEST=1 go test ./tests/ -run "TestShellScenariosAgainstBash/<scenario_name>" -timeout 120s -v

Step 8: Review unnecessary Windows-specific assertions

Scan all scenario tests for the target that use Windows-specific assertion fields and evaluate whether they are actually needed.

grep -rl "stdout_windows\|stderr_windows\|stdout_contains_windows\|stderr_contains_windows" tests/scenarios/cmd/<target>/ 2>/dev/null
grep -rl "stdout_windows\|stderr_windows\|stdout_contains_windows\|stderr_contains_windows" tests/scenarios/shell/<target>/ 2>/dev/null

For each test with Windows-specific assertions:

1. Read the test and compare the Windows-specific field value against the non-Windows field value
2. Evaluate whether the difference is genuine: Windows-specific assertions are only needed when output genuinely differs on Windows — typically:
   • Path separators (\ vs /)
   • Line endings (\r\n vs \n)
   • OS-specific error messages
   • Windows reserved filenames (CON, PRN, NUL, etc.)
3. Classify the result:

For each unnecessary Windows-specific assertion removed, the non-Windows assertion serves as the fallback and will be used on all platforms.

Step 9: Fix failing tests

Run the /fix-ci-tests skill to verify all tests pass and fix any failures. This will:

• Run scenario tests and Go tests
• Run bash comparison tests
• Fix test expectations or shell implementation as needed
• Re-run until all tests pass

If skip_assert_against_bash: true is added to any test, ensure a YAML comment explains why.

Step 10: Commit, push, and post report

After all tests pass for the current target, commit, push, and post a coverage report.

1. Commit and push

# Stage all new and modified test scenario files
git add tests/scenarios/

# Commit with a descriptive message
git commit -m "test: improve coverage for <target>

Add scenario tests to improve coverage. See PR comment for full report.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>"

# Push to the current branch
git push

If the push fails (e.g. no upstream branch), set the upstream:

git push -u origin "$(git branch --show-current)"

2. Determine the PR number

gh pr view --json number --jq '.number'

If no PR exists for the current branch, skip posting and print the report to the console instead.

3. Build and post the report

Compose the report and post it as a PR comment:

## Coverage Improvement Summary — `<target>`

**Target**: <command or feature>
**Reference suites consulted**: <list>

### New tests added
| File | Category | Description |
|------|----------|-------------|
| ... | ... | ... |

### Coverage before/after
- Before: N scenario tests
- After: M scenario tests (+X new)
- New categories covered: <list>

### Cleanup
- Duplicate tests removed: <count>
- `skip_assert_against_bash` flags removed: <count>
- Unnecessary Windows-specific assertions removed: <count>

### Findings
- <any shell bugs discovered>
- <any intentional divergences noted>

---
🤖 Generated with [Claude Code](https://claude.com/claude-code)

gh pr comment <PR_NUMBER> --body "$(cat <<'EOF'
<report content here>
EOF
)"

If posting fails (e.g. permissions), print the report to the console as a fallback.

4. Proceed to next target

After posting, move to the next target in the list and start its Step 3. Continue until all targets are processed.