Gradle: No tests found

I faced this exact issue today. Please do feel free to use all the other worthy solutions as mentioned above but what specifically worked for me was to delete the ".gradle" folder (found under the project panel on the left in Android Studio) entirely, followed by a clean build. A simple clean build didn't work for me.

I had the issue, try upgrading the test runner. Upgrading it to 0.5 from 0.4.x solved it. Ensure you have these lines in your build.gradle:

androidTestCompile "junit:junit:4.12"
androidTestCompile "com.android.support.test:runner:0.5"

One possible reason for this error message is that you get a crash in the app early in the test Runner. In such cases the exception stack will be in logcat but not in the gradle output.