Conflict with dependency 'com.android.support:support-annotations' in project ':app'. Resolved versions for app (26.1.0) and test app (27.1.1) differ. See https://d.android.com/r/tools/test-apk-dependency-conflicts.html for details. Information:Gradle tasks [:app:generateDebugSources, :app:generateDebugAndroidTestSources, :app:mockableAndroidJar]

解决方案：在此行添加gradle模块的依赖项
compile 'com.android.support:support-annotations:27.1.1'
如果您使用的是Android工作室3+改变compile到implementation