Write resilient test assertions

Write test assertions that are resilient to implementation changes by focusing on behavior rather than implementation details. Avoid exact matches when partial or behavioral assertions would suffice.

Key practices:

1. Use flexible matchers instead of exact equality
2. Focus on behavior over implementation details
3. Test for presence of required properties rather than exact object shape

Example - Instead of brittle exact matching:

// ❌ Brittle - breaks if new options are added
expect(options).toEqual({ 
  preview: false, 
  viewColumn: vscode.ViewColumn.Active 
})

// ✅ Resilient - verifies required properties
expect(options).toEqual(expect.objectContaining({ 
  preview: false,
  viewColumn: vscode.ViewColumn.Active 
}))

For token counting or similar approximate values:

// ❌ Brittle - breaks if tokenizer changes slightly
expect(tokenCount).toBe(14)

// ✅ Resilient - verifies reasonable range
expect(tokenCount).toBeGreaterThan(12)
expect(tokenCount).toBeLessThan(16)

This approach:

• Reduces test maintenance as implementation details change
• Focuses tests on behavioral requirements
• Makes tests more reliable and meaningful
• Avoids over-mocking that tests the mocks rather than the code