fix: language breaking change

[illusory0x0]

No description provided.

[peter-jerry-ye-code-review]

Changed failure function call from fail!() to fail()

Category
Correctness
Code Snippet
fail!("@lib.hello() != "Hello, world!"")
Recommendation
Verify that fail() is the correct function name in MoonBit's testing framework. If this is a breaking change, ensure all test files are updated accordingly.
Reasoning
The removal of the exclamation mark suggests either a syntax correction or an API change in the testing framework. Since this is a test assertion, it's critical to ensure the correct failure function is being used to properly report test failures.

Test error message contains redundant string literal

Category
Maintainability
Code Snippet
fail("@lib.hello() != "Hello, world!"")
Recommendation
Consider extracting the expected value into a constant:

let EXPECTED = "Hello, world!"
if @lib.hello() != EXPECTED {
  fail("Expected '${EXPECTED}' but got '${@lib.hello()}'")
}

Reasoning
The current error message duplicates the string literal. Using a constant and interpolated string would make the test more maintainable and provide better failure messages by showing both expected and actual values.