test: expand frontmatter tests to cover all exported functions

[GoBeromsu]

Summary

This PR expands the test coverage for src/frontmatter/index.ts to include comprehensive tests for all exported functions:

• getContentWithoutFrontmatter: 5 test cases covering frontmatter extraction, edge cases with empty content, content with only frontmatter, and multiline content
• getFrontmatterSetting: 8 test cases covering successful retrieval and error scenarios (missing ID, empty/null/undefined settings arrays)
• getFieldValues: 9 test cases with complete Obsidian MetadataCache mocking, covering regular fields, tags field special handling, duplicate removal, and single/array value handling
• insertToFrontMatter: 11 test cases covering Normal and WikiLink types, overwrite modes, duplicate removal, empty string filtering, and field creation

Changes

New Files

• __tests__/frontmatter/index.test.ts: Comprehensive test suite with 32 passing test cases

Modified Files

• __mocks__/obsidian.ts: Added required Obsidian API mocks:
  • getFrontMatterInfo: Parses frontmatter boundaries
  • parseFrontMatterStringArray: Extracts field values from frontmatter
  • getAllTags: Collects tags from frontmatter and inline content
  • MetadataCache class: Mocks file metadata caching
  • TFile class: Basic file object for testing

Test Results

All 32 new tests pass successfully:

• Total test suites: 10 passed
• Total tests: 145 passed (113 existing + 32 new)
• Test execution time: ~0.37s

Test Coverage Details

getContentWithoutFrontmatter (5 tests)

• Removes frontmatter from content with frontmatter
• Returns full content when no frontmatter exists
• Handles empty content
• Handles content with only frontmatter
• Handles multiline content after frontmatter

getFrontmatterSetting (8 tests)

• Returns correct setting when ID exists
• Returns settings for different ID positions
• Throws error when ID does not exist
• Throws error when settings array is empty
• Throws error when settings is undefined/null
• Verifies all field properties are intact

getFieldValues (9 tests)

• Collects unique values for regular frontmatter fields
• Handles tags field using getAllTags
• Returns empty array when no files provided
• Skips files with no cache
• Skips files without the specified field
• Removes duplicate values across files
• Handles single value and array values correctly
• Handles empty frontmatter
• Maintains unique values with Set behavior

insertToFrontMatter (11 tests)

• Inserts values with Normal link type
• Inserts values with WikiLink format
• Overwrites existing values when overwrite is true
• Appends values when overwrite is false
• Removes duplicate values
• Filters out empty strings
• Creates new field if it does not exist
• Handles WikiLink with overwrite and deduplication
• Returns Promise that resolves
• Handles empty value array

Quality Assurance

• All tests follow existing test patterns in the codebase
• Mocks use the established patterns from __mocks__/obsidian.ts
• Tests are isolated and do not depend on external state
• Each function has comprehensive coverage including edge cases and error scenarios
• Tests verify both successful operations and error conditions

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