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Trail of Bits Blog·27d ago·5 min read
Mutation testing comes to DAML
TL;DR
DAML's test coverage reports can be misleading, as they only indicate code execution without verifying outcomes. Mewt, an open-source mutation-testing engine, now supports DAML, generating mutants to assess test suite effectiveness.
✦ Why It Matters
Engineers should integrate Mewt into their DAML projects to identify and address gaps in their test coverage immediately.
Key Takeaways
- Install Mewt to enhance your DAML testing process.
- Use mutation testing to identify untested scenarios in your code.
- Focus on surviving mutants to improve test suite effectiveness.
- Regularly audit your tests to catch potential bugs early.
Full Summary
Test coverage in smart-contract development often provides a false sense of security, as it only shows which lines of code were executed without confirming if the tests would catch failures. Mewt, a mutation-testing engine, has been enhanced to support DAML, the programming language for Canton Network applications.
It generates mutants—modified versions of the code with small changes—and runs existing test suites against them. By counting how many mutants survive, developers can gauge the effectiveness of their tests.
Unlike traditional coverage metrics, which can report 100% coverage without ensuring test quality, mutation testing highlights specific areas where tests are lacking. This method has previously uncovered significant bugs that standard tests missed, emphasizing its value in improving software reliability.