Assert exact expectations

Always assert exact expected values in tests rather than using loose assertions. When testing the presence of elements or count of items, use equality assertions (`assert_eq!`) instead of non-empty checks (`assert!(!items.is_empty())`) or inequality assertions (`assert!(items.len() >= 2)`).

copy reviewer prompt

Prompt

Reviewer Prompt
Deploy Agent

Always assert exact expected values in tests rather than using loose assertions. When testing the presence of elements or count of items, use equality assertions (assert_eq!) instead of non-empty checks (assert!(!items.is_empty())) or inequality assertions (assert!(items.len() >= 2)).

Exact assertions:

  • Make test failures more informative by showing the expected and actual values
  • Prevent silent test degradation when code changes affect output quantity
  • Catch unexpected behavior that looser assertions would miss

For example, instead of:

// Testing that some tokens exist (too loose)
let class_tokens = tokens.iter()
    .filter(|t| matches!(t.token_type, SemanticTokenType::Class))
    .collect();
assert!(!class_tokens.is_empty());

// Using inequality (can hide issues)
let variable_tokens = tokens.iter()
    .filter(|t| matches!(t.token_type, SemanticTokenType::Variable))
    .collect();
assert!(variable_tokens.len() >= 2);

Use this approach instead:

// Test for the exact expected count
let class_tokens = tokens.iter()
    .filter(|t| matches!(t.token_type, SemanticTokenType::Class))
    .collect();
assert_eq!(class_tokens.len(), 1);

// Or use a helper function for multiple assertions
assert_token_count([
    (SemanticTokenType::BuiltinConstant, 3),
    (SemanticTokenType::Variable, 3),
]);

When practical, consider extracting assertions into helper functions that verify the exact composition of test results, making tests more readable and consistent.

Source discussions