What is the most important key metric for evaluating the effectiveness of automated tests?

The most important metric for evaluating the effectiveness of automated tests is code coverage. It shows what portion of the application's code is tested by the tests, helping to identify untested areas and improve testing quality.

However, besides coverage, other metrics are also important:

• Percentage of successful tests — how stable the tests are.
• Test execution time — affects feedback speed.
• Number of false positives — affects trust in the tests.

Ultimately, code coverage is a key metric, but it should be considered together with the quality and stability of the tests.