[test-improver] Improve tests for config/rules package

[github-actions]

File Analyzed

• Test File: internal/config/rules/rules_test.go
• Package: internal/config/rules
• Lines of Code: ~794 → 816 (+22 net, 35 insertions / 13 deletions)

Improvements Made

1. Better Testify Patterns: require.NotNil for *ValidationError return types

The validation functions (PortRange, TimeoutPositive, MountFormat, NonEmptyString, AbsolutePath) all return *ValidationError, not the standard error interface. Using require.Error(t, err) on a *ValidationError value hits Go's interface-nil gotcha: a nil *ValidationError passed to a function accepting error produces a non-nil interface (type info present, value nil), so require.Error would incorrectly pass even when the function returned nil.

Replaced all 5 occurrences with require.NotNil(t, err, ...) which correctly uses reflection to detect nil pointers.

2. Fail-Fast on Unexpected Success: require.Nil over assert.Nil

Changed assert.Nil(t, err, "Unexpected error") → require.Nil(t, err, "Unexpected validation error") at all 5 success-path locations. When a validation function unexpectedly returns an error, require stops the test immediately rather than continuing (which could cause confusing nil-dereference panics or misleading follow-up failures).

3. Increased Coverage: TestValidationError_Error negative assertion

Added notWantSubstr field and assert.NotContains checks to TestValidationError_Error. The "error without suggestion" test case now explicitly verifies that the string "Suggestion:" is absent from the error message, confirming the conditional rendering in ValidationError.Error() works correctly in both directions.

4. Increased Coverage: Edge cases for TestAbsolutePath

Added two missing edge cases for the AbsolutePath validator:

Input	Description	Expected
"C:"	Windows-like path, too short (len=2, needs ≥3)	Error: must be absolute
"C"	Single drive letter, too short (len=1)	Error: must be absolute

These cover the len(value) >= 3 boundary condition in the Windows path detection logic, which was previously untested.

Test Execution

Tests cannot be run in this environment due to sandbox restrictions on binary execution. All changes are backward-compatible: no existing tests were removed or modified in logic, only improved in assertion style, with new test cases added.

Why These Changes?

rules_test.go was selected because it contained the most non-idiomatic testify usage in the codebase: five assert.Nil calls that should be require.Nil (fail-fast), and five require.Error calls that silently pass Go's interface-nil pitfall when used with concrete pointer types. The additional edge cases cover boundary conditions in AbsolutePath that were previously untested.

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Focuses on better patterns, increased coverage, and more stable tests

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Pull request overview

This PR improves the robustness and coverage of the internal/config/rules test suite by updating assertions to correctly handle validators that return *ValidationError (a concrete pointer type) and by adding a few missing edge cases.

Changes:

• Replace require.Error/assert.Nil patterns with require.NotNil/require.Nil to avoid the Go “typed-nil to interface” pitfall and to fail fast on unexpected successes.
• Extend TestValidationError_Error to assert the absence of the “Suggestion:” section when Suggestion is empty.
• Add additional boundary test cases for AbsolutePath Windows-drive inputs ("C:" and "C").

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