com.android.support:support-annotations 에러

Error:Execution failed for task ':app:preDebugAndroidTestBuild'.

> Conflict with dependency 'com.android.support:support-annotations' in project ':app'. Resolved versions for app (25.2.0) and test app (25.4.0) differ. See https://d.android.com/r/tools/test-apk-dependency-conflicts.html for details.

app단의 gradle 파일에 가서 아래 부분을 

androidTestImplementation 'com.android.support.test:runner:1.0.1'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'

다음과 같이 바꿔 준다

androidTestImplementation('com.android.support.test:runner:1.0.1', {
    exclude group: 'com.android.support', module: 'support-annotations'
})
androidTestImplementation('com.android.support.test.espresso:espresso-core:3.0.1', {
    exclude group: 'com.android.support', module: 'support-annotations'
})

이유는 나중에 찾고 일단 봉합완료...