[test] Add tests for config.unmarshalStringListOrExpression

[github-actions]

Test Coverage Improvement: unmarshalStringListOrExpression

Function Analyzed

• Package: internal/config
• Function: unmarshalStringListOrExpression (and related helpers in guard_policy.go)
• Previous Coverage: unmarshalStringListOrExpression 89.5%, GuardPolicy.UnmarshalJSON 0%, GuardPolicyToMap 0%
• New Coverage: All three functions at 100%
• Complexity: Medium — two early-return error branches, delimiter splitting with trim-and-filter loop

Why This Function?

unmarshalStringListOrExpression had two untested error paths that could not be reached by existing tests:

1. Line 289 — triggered when the JSON value is neither a []string array nor a string (e.g. a JSON number, boolean, or object). No existing test passed such a value through refusal-labels.
2. Line 296 — triggered when the expression string consists entirely of delimiter characters (comma or newline), so strings.FieldsFunc returns zero parts. The existing test for " " (spaces only) skipped this branch because spaces are not delimiters; it fell through to the second empty-result check instead.

GuardPolicy.UnmarshalJSON and GuardPolicyToMap also had uncovered error paths (non-object JSON input, typed-nil-pointer marshalling to null) that are now covered.

Tests Added

New file: internal/config/guard_policy_str_expr_test.go

• ✅ TestUnmarshalStringListOrExpression (15 table-driven cases)
  • Happy path: JSON array, empty array, comma-delimited string, newline-delimited string, mixed delimiters with whitespace, single label
  • Error path (line 289): JSON number, boolean, object, array-of-integers
  • Error path (line 296): comma-only string, newline-only string, multiple-commas-only
  • Error path (line 308): spaces-around-commas, whitespace-only string
• ✅ TestGuardPolicyUnmarshalJSON_NonObjectJSON (3 cases) — covers line 100–102
• ✅ TestGuardPolicyToMap_TypedNilPointer (1 case) — covers line 175–177 via typed nil marshalling to null
• ✅ TestAllowOnlyPolicyUnmarshalJSON_RefusalLabelsInvalidType (5 cases) — exercises both new error paths end-to-end through AllowOnlyPolicy.UnmarshalJSON

Coverage Report

Before:
  unmarshalStringListOrExpression   89.5%
  GuardPolicy.UnmarshalJSON          0.0%   (line 100-102 uncovered)
  GuardPolicyToMap                   0.0%   (line 175-177 uncovered)

After:
  unmarshalStringListOrExpression  100.0%
  GuardPolicy.UnmarshalJSON        100.0%
  GuardPolicyToMap                 100.0%

Test Execution

All 24 new sub-tests pass:

--- PASS: TestUnmarshalStringListOrExpression (0.00s)
--- PASS: TestGuardPolicyUnmarshalJSON_NonObjectJSON (0.00s)
--- PASS: TestGuardPolicyToMap_TypedNilPointer (0.00s)
--- PASS: TestAllowOnlyPolicyUnmarshalJSON_RefusalLabelsInvalidType (0.00s)
ok  github.com/github/gh-aw-mcpg/internal/config  1.633s

---

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[Copilot]

Pull request overview

This PR improves test coverage in internal/config by adding a dedicated test file that exercises previously uncovered branches in unmarshalStringListOrExpression and related guard-policy JSON helpers.

Changes:

• Add table-driven unit tests that cover valid inputs and multiple invalid-type / delimiter-only error paths for unmarshalStringListOrExpression.
• Add tests for GuardPolicy.UnmarshalJSON rejecting non-object JSON payloads.
• Add a test covering GuardPolicyToMap behavior when passed a typed-nil pointer that marshals to JSON null.

Show a summary per file

File	Description
internal/config/guard_policy_str_expr_test.go	Adds new unit tests to reach previously uncovered error branches in guard policy parsing/mapping helpers.

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• Files reviewed: 1/1 changed files
• Comments generated: 4