Sometimes IDE imports the namespace with Test automatically for return data type like string, float etc or any other means.
Time to time we're getting issue with running tests on PRs in magento/magento2 repository because someone imported \Magento\Tests\NamingConvention\true\string by mistake. As result - we have "No build reports available" for "Database Compare build", "Functional Tests build", "Sample Data Tests build" while Static tests are shown as "failing" but in results - we don't really have reason
Any occurrence starts with Magento\Tests in import from the namespace will raise the warning.
Remove Magento\Tests from the imported namespaces