[test-improver] Improve tests for config package

[github-actions]

Test Improvements: validation_test.go

File Analyzed

• Test File: internal/config/validation_test.go
• Package: internal/config
• Lines of Code: 616 → 697 (added comprehensive test coverage)
• Test Functions: 7 → 8 (added new test for container variable expansion)

Improvements Made

1. Better Testing Patterns ✅

• ✅ Replaced all manual strings.Contains() error checks with assert.ErrorContains()
• ✅ Converted os.Setenv()/defer os.Unsetenv() to t.Setenv() for automatic cleanup
• ✅ Replaced manual map key-value comparison loops with assert.Equal()
• ✅ Created setupStdinTest() helper function to reduce boilerplate from ~10 lines to 1-2 lines per test
• ✅ Removed unused strings import after refactoring
• ✅ Consistent use of require.Error() for critical assertions

2. Increased Coverage ✅

• ✅ Added test for nested variables in paths: /path/${VAR1}/subdir/${VAR2}
• ✅ Added test for empty variable values
• ✅ Added test for variables at start and end of strings
• ✅ Added test for empty env map (no variables to expand)
• ✅ Added test for static values with no variable expansion
• ✅ Added test for malformed JSON input to LoadFromStdin()
• ✅ Added test for empty mcpServers map
• ✅ Added test for variable expansion in container field (TestLoadFromStdin_VariableExpansionInContainer)
• ✅ Test Cases: ~50 → ~60 total test cases (+20% increase)

Coverage Improvement:

• Better edge case coverage for variable expansion logic
• More robust error path testing
• Comprehensive validation of stdin loading scenarios

3. Cleaner & More Stable Tests ✅

• ✅ Helper Function: Extracted stdin test setup into reusable setupStdinTest() helper
  • Handles pipe creation, goroutine spawning, and cleanup
  • Uses t.Helper() for better test failure reporting
  • Returns cleanup function for use with defer
• ✅ Automatic Cleanup: All environment variables now use t.Setenv() (Go 1.17+)
  • No more forgotten defer os.Unsetenv() calls
  • Automatic cleanup even on test panics
• ✅ Consistent Assertions: All tests now use testify best practices
  • require.Error() for critical checks (stops test on failure)
  • assert.ErrorContains() for error message validation
  • assert.Equal() for value comparisons

Code Quality Metrics

Before:

// Manual error checking (verbose, inconsistent)
if err != nil && !strings.Contains(err.Error(), expectedMsg) {
    t.Errorf("Expected error containing %q, got: %v", expectedMsg, err)
}

// Manual stdin setup (10+ lines, repeated 3 times)
r, w, _ := os.Pipe()
oldStdin := os.Stdin
os.Stdin = r
go func() {
    w.Write([]byte(jsonConfig))
    w.Close()
}()
// ... test code ...
os.Stdin = oldStdin

After:

// Clean testify assertions (concise, consistent)
require.Error(t, err)
assert.ErrorContains(t, err, expectedMsg)

// Simple helper usage (1 line + defer)
cleanup := setupStdinTest(t, jsonConfig)
defer cleanup()

Test Execution

All improvements maintain 100% backward compatibility with existing tests. The changes are focused on:

• Maintainability: Easier to add new tests with helper functions
• Readability: Clear, concise assertions using testify idioms
• Reliability: Automatic cleanup prevents test pollution
• Coverage: More edge cases = more robust code

Why These Changes?

This test file was selected based on analysis showing:

1. High improvement potential: 9/10 score from code analysis
2. Manual error checking: Multiple instances of verbose strings.Contains() patterns
3. Repetitive boilerplate: Stdin setup code duplicated 3 times
4. Coverage gaps: Missing edge cases for variable expansion and JSON parsing
5. High impact: Config validation is critical infrastructure code

The improvements make the test suite:

• Easier to maintain: Less boilerplate, consistent patterns
• More comprehensive: Better edge case coverage
• More reliable: Automatic cleanup, better assertions
• More readable: Clear intent with testify idioms

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

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