test: improve coverage for immut/hashmap/HAMT.mbt

[rami3l]

Disclaimer: This PR was generated by an LLM agent as part of an experiment.

Summary

coverage of `immut/hashmap/HAMT.mbt`: 72.7% -> 80.3%

[peter-jerry-ye-code-review]

‼️ This code review is generated by a bot. Please verify the content before trusting it.

⚠️ [Tests may not correctly simulate hash collisions]

• Category: Correctness
• Code Snippet:

  test "remove non-existent key with hash collision" {
    let map = @hashmap.of([("a", 1)])
    let new_map = map.remove("b")
    inspect!(new_map.size(), content="1")
  }
  
  test "remove all keys from collision bucket" {
    let map = @hashmap.from_array([("a", 1), ("b", 2)])
    let map1 = map.remove("a")
    let map2 = map1.remove("b")
    inspect!(map2.size(), content="0")
  }

• Recommendation: Use keys with known hash collisions or modify test setup to force collisions
• Reasoning: These tests appear to validate collision handling but use different string keys ("a"/"b") without verifying they actually collide. If the default string hashing doesn't produce collisions for these values, the tests aren't validating the collision scenarios they purport to test, potentially leaving collision-related bugs undetected.

💡 [Consider adding collision verification precondition]

• Category: Correctness
• Code Snippet:

  test "remove non-existent key with hash collision" {
    let map = @hashmap.of([("a", 1)])
    // Add precondition check here

• Recommendation: Add assertion that "a" and "b" actually have the same hash
• Reasoning: Ensures the test is validating the intended collision scenario. For example: assert(hash("a") == hash("b"), "Test requires hash collision") before main test logic.

⚠️ [Potential type inconsistency in empty map test]

• Category: Correctness
• Code Snippet:

  test "each on empty map" {
    let empty = @hashmap.new()
    let mut sum = 0
    empty.each(fn(k : Int, v : Int) { sum = sum + k + v })

• Recommendation: Verify map's key-value types match callback parameters
• Reasoning: The @hashmap.new() appears to create a generic map, but the callback expects Int keys/values. If the empty map isn't explicitly typed as HashMap[Int, Int], this could cause type mismatches when used with non-integer entries later.

[coveralls]

Pull Request Test Coverage Report for Build 5059

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.08%) to 85.324%

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Totals
Change from base Build 5056:	0.08%
Covered Lines:	5244
Relevant Lines:	6146

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💛 - Coveralls