[test-improver] Improve tests for guard package (normalizeLabelListField)

[github-actions]

File Analyzed

• Test File: internal/guard/wasm_payload_test.go
• Package: internal/guard
• Lines Added: +123

Improvements Made

1. Added TestNormalizeLabelListField

The normalizeLabelListField helper in wasm_payload.go had no dedicated unit tests and sat at 82.6% coverage (4 branches uncovered). Tests for this function were entirely indirect — exercised only through buildStrictLabelAgentPayload in wasm_test.go.

Added a comprehensive, table-driven TestNormalizeLabelListField directly targeting the function:

normalizeLabelListField: 82.6% → 100%
internal/guard package:  92.0% → 92.5%

2. Increased Coverage — Previously Uncovered Branches

Branch	Input	Reason Not Covered
return nil, fmt.Errorf("...expected array of strings or comma/newline-delimited string...")	raw = 42 (integer)	Never tested with non-string, non-array input
return nil, fmt.Errorf("...must include at least one non-empty label") (first)	raw = ","	Never tested with delimiter-only string
if trimmed == "" { continue }	raw = "valid, ,other"	Never tested with whitespace-only intermediate part
return nil, fmt.Errorf("...must include at least one non-empty label") (second)	raw = " "	Never tested with all-whitespace string

3. Test Cases Added (17 subtests)

Array path:

• Valid array → trimmed labels returned
• Empty array → empty slice
• Array with empty string entry → error
• Array with non-string entry → error

Non-array, non-string path (previously 0% covered):

• Integer input → error
• Boolean input → error

String path:

• Comma-delimited string → split labels
• Newline-delimited string → split labels
• Mixed comma and newline delimiters
• Leading/trailing whitespace trimmed per label
• Single label string

String path error cases (previously 0% covered):

• Empty string → error
• Comma-only string → error
• Newline-only string → error
• Whitespace-only string → error (hits both continue and len(out)==0 branches)
• Comma-delimited whitespace-only parts → error

Mixed case:

• Whitespace-only part among valid parts is skipped (hits continue, result non-empty)

4. Better Test Structure

• ✅ Used t.Parallel() at top level and in each subtest for faster execution
• ✅ Table-driven pattern with clear name, raw, want, wantErr fields
• ✅ Comments explaining which branches each case covers
• ✅ Consistent use of require for fatal checks, assert for informational checks

Test Execution

=== RUN   TestNormalizeLabelListField
--- PASS: TestNormalizeLabelListField (0.00s)
    --- PASS: .../valid_array_returns_trimmed_labels (0.00s)
    --- PASS: .../empty_array_returns_empty_slice (0.00s)
    --- PASS: .../array_with_empty_string_entry_returns_error (0.00s)
    --- PASS: .../array_with_non-string_entry_returns_error (0.00s)
    --- PASS: .../integer_value_is_not_array_or_string (0.00s)
    --- PASS: .../bool_value_is_not_array_or_string (0.00s)
    --- PASS: .../comma-delimited_string_returns_split_labels (0.00s)
    --- PASS: .../newline-delimited_string_returns_split_labels (0.00s)
    --- PASS: .../mixed_comma_and_newline_delimiters (0.00s)
    --- PASS: .../leading_and_trailing_whitespace_trimmed_from_each_label (0.00s)
    --- PASS: .../single_label_string (0.00s)
    --- PASS: .../empty_string_returns_error (0.00s)
    --- PASS: .../string_with_only_a_comma_delimiter_returns_error (0.00s)
    --- PASS: .../string_with_only_newline_delimiter_returns_error (0.00s)
    --- PASS: .../whitespace-only_string_returns_error (0.00s)
    --- PASS: .../comma-delimited_whitespace-only_parts_returns_error (0.00s)
    --- PASS: .../whitespace-only_part_among_valid_parts_is_skipped (0.00s)

ok  github.com/github/gh-aw-mcpg/internal/guard  0.077s  coverage: 92.5%

All 26 package tests pass (including the 17 new subtests).

Why These Changes?

normalizeLabelListField is a security-relevant helper that validates and normalizes the refusal-labels field in guard policies used to control tool call behavior. Having comprehensive direct unit tests for this function:

1. Makes the validation semantics explicit and self-documenting
2. Ensures edge cases (whitespace, mixed delimiters, wrong types) behave correctly
3. Improves confidence when modifying label parsing logic in the future

The existing indirect coverage through buildStrictLabelAgentPayload only exercised the happy paths, leaving 4 error branches entirely untested.

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Pull request overview

Adds direct, table-driven unit coverage for the internal/guard helper normalizeLabelListField, making label parsing/validation behavior explicit and fully exercised (including previously uncovered error branches).

Changes:

• Added TestNormalizeLabelListField with comprehensive table-driven coverage across array/string/invalid-type inputs.
• Increased branch coverage for delimiter/whitespace edge cases and invalid inputs.

Show a summary per file

File	Description
internal/guard/wasm_payload_test.go	Adds dedicated unit tests for normalizeLabelListField, covering success paths and previously uncovered error/edge branches.

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• Files reviewed: 1/1 changed files
• Comments generated: 2
• Review effort level: Low