isUseDefaultListeners

Whether the default listeners and reporters should be used. Since Gradle 1.4 it defaults to 'false' so that Gradle can own the reports generation and provide various improvements. This option might be useful for advanced TestNG users who prefer the reports generated by the TestNG library. If you cannot live without some specific TestNG reporter please use listeners property. If you really want to use all default TestNG reporters (e.g. generate the old reports):

plugins {
    id 'java'
}

test {
    useTestNG() {
        // report generation delegated to TestNG library:
        useDefaultListeners = true
    }

    // turn off Gradle's HTML report to avoid replacing the
    // reports generated by TestNG library:
    reports.html.required = false
}
Please refer to the documentation of your version of TestNG what are the default listeners. At the moment of writing this documentation, the default listeners are a set of reporters that generate: TestNG variant of HTML results, TestNG variant of XML results in JUnit format, emailable HTML test report, XML results in TestNG format.