Modernize sliceutil tests to use testify assertions

[Copilot]

The pkg/sliceutil/sliceutil_test.go file used manual if result != expected checks with t.Error() calls instead of testify assertions, inconsistent with repository standards documented in specs/testing.md.

Changes

• Import: Added github.com/stretchr/testify/assert
• Table-driven tests: Converted manual checks to assert.Equal(t, expected, result, message) in:
  • TestContains
  • TestContainsAny
  • TestContainsIgnoreCase
  • TestContainsIgnoreCase_Unicode
• Edge case tests: Converted manual conditionals to assert.True()/assert.False() in:
  • TestContains_LargeSlice
  • TestContains_SingleElement
  • TestContainsAny_MultipleMatches
  • TestContainsAny_NilSubstrings
  • TestContainsIgnoreCase_PartialMatch
  • TestContains_Duplicates
  • TestContainsAny_OrderMatters
• Messages: Standardized assertion messages to "should [expected behavior]" pattern

Example

// Before
result := Contains(tt.slice, tt.item)
if result != tt.expected {
    t.Errorf("Contains(%v, %q) = %v; want %v", tt.slice, tt.item, result, tt.expected)
}

// After
result := Contains(tt.slice, tt.item)
assert.Equal(t, tt.expected, result,
    "Contains should return correct value for slice %v and item %q", tt.slice, tt.item)

Reduced code by 35 lines while improving test failure diagnostics and maintainability.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[testify-expert] Improve Test Quality: ./pkg/sliceutil/sliceutil_test.go</issue_title>
<issue_description>## Overview

The test file ./pkg/sliceutil/sliceutil_test.go has been selected for quality improvement by the Testify Uber Super Expert. This test file demonstrates excellent table-driven test structure and comprehensive coverage, but it uses manual error checking (if result != expected) instead of testify assertions. Modernizing to use testify will provide clearer error messages, better test output, and align with the repository's testing standards documented in specs/testing.md.

Current State

• Test File: ./pkg/sliceutil/sliceutil_test.go
• Source File: ./pkg/sliceutil/sliceutil.go
• Test Functions: 15 test functions (including benchmarks)
• Lines of Code: 378 lines
• Source Functions: 3 exported functions (100% tested)

Test Quality Analysis

Strengths ✅

1. Excellent table-driven test structure - All main tests (TestContains, TestContainsAny, TestContainsIgnoreCase) use proper table-driven patterns with descriptive test case names
2. Comprehensive edge case coverage - Tests cover empty slices, nil values, empty strings, unicode, duplicates, and large data sets
3. Performance benchmarks - Includes benchmark tests for all three functions
4. Good test organization - Tests are well-organized with clear separation between table-driven tests and additional edge case tests

Areas for Improvement 🎯

1. Testify Assertions

Current Issues:

• All tests use manual if result != expected checks with t.Error() or t.Errorf()
• Manual error checking is verbose and provides less context than testify assertions
• No distinction between setup failures (should use require) and test validations (should use assert)

Recommended Changes:

// ❌ CURRENT (manual checks)
result := Contains(tt.slice, tt.item)
if result != tt.expected {
    t.Errorf("Contains(%v, %q) = %v; want %v", tt.slice, tt.item, result, tt.expected)
}

// ✅ IMPROVED (testify)
result := Contains(tt.slice, tt.item)
assert.Equal(t, tt.expected, result, "Contains should return correct value for slice %v and item %q", tt.slice, tt.item)

// Alternative (more explicit)
if tt.expected {
    assert.True(t, result, "Contains should find %q in slice %v", tt.item, tt.slice)
} else {
    assert.False(t, result, "Contains should not find %q in slice %v", tt.item, tt.slice)
}

Why this matters:

• Testify provides clearer, more actionable error messages when tests fail
• The repository standard (per specs/testing.md) requires testify assertions
• Better integration with testing tools and IDEs
• Clearer distinction between critical setup (require.*) and validations (assert.*)

2. Import Statement

Current Issue:

• Missing testify import: "github.com/stretchr/testify/assert"

Recommended Change:

import (
    "testing"
    
    "github.com/stretchr/testify/assert"
)

3. Edge Case Tests - Use Table-Driven Pattern

Current Issues:

• Edge case tests like TestContains_LargeSlice, TestContains_SingleElement, etc. use manual assertions
• These could benefit from testify's clearer error messages

Recommended Improvements:

Example 1: TestContains_LargeSlice

// ❌ CURRENT
if !Contains(largeSlice, "a") {
    t.Error("Expected to find 'a' at beginning of large slice")
}

// ✅ IMPROVED
assert.True(t, Contains(largeSlice, "a"), "should find 'a' at beginning of large slice")
// OR even better:
assert.Contains(t, largeSlice, "a", "should find 'a' at beginning of large slice")

Example 2: TestContains_SingleElement

// ❌ CURRENT
slice := []string{"single"}
if !Contains(slice, "single") {
    t.Error("Expected to find item in single-element slice")
}
if Contains(slice, "other") {
    t.Error("Expected not to find different item in single-element slice")
}

// ✅ IMPROVED
slice := []string{"single"}
assert.True(t, Contains(slice, "single"), "should find item in single-element slice")
assert.False(t, Contains(slice, "other"), "should not find different item in single-element slice")

Example 3: TestContainsAny_MultipleMatches

// ❌ CURRENT
if !ContainsAny(s, "quick", "lazy") {
    t.Error("Expected to find at least one matching substring")
}

// ✅ IMPROVED
assert.True(t, ContainsAny(s, "quick", "lazy"), "should find at least one matching substring")

Example 4: TestContainsIgnoreCase_PartialMatch

// ❌ CURRENT
if !ContainsIgnoreCase(s, "hub") {
    t.Error("Expected to find partial match 'hub' in 'GitHub'")
}

// ✅ IMPROVED
assert.True(t, ContainsIgnoreCase(s, "hub"), "should find partial match 'hub' in 'GitHub'")

4. Consider assert.Contains for Slice Checks

Current Pattern:

result := Contains(tt.slice, tt.item)
assert.Equal(t, tt.expected, result, ...)

**Alternative (when expecting ...

• Fixes [testify-expert] Improve Test Quality: ./pkg/sliceutil/sliceutil_test.go #9932

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