Cannot resolve symbol 'AndroidJUnit4'

Make sure your app in debug build variant. Go to Build > Select Build Variant... and the following should show up:

I made the mistake to put the test classes at src/test. After moving them to src/androidTest/java/ the dependency was resolved.

Update

The Android Test Library is now part of AndroidX. Be sure to use the correct Gradle dependencies found in the official documentation.

Original Answer

I found here that there are newer versions of the Testing Support Library than what I was using:

dependencies {
    androidTestCompile 'com.android.support.test:runner:0.5'
    androidTestCompile 'com.android.support.test:rules:0.5'
    androidTestCompile 'com.android.support.test.uiautomator:uiautomator-v18:2.1.2'
}

Note: Be sure to use the most recent versions of these libraries. This question is from a time when the Android Test Support Library was new and the version numbers here are very out of date.

Ok so here is your mistake and mine!

If we are going to write a pice of code for Local Unit Testing we shouldn't use @RunWith(AndroidJUnit4.class) cause we do not use AndroidJUnit4 but we need Junit4. so we should write @RunWith(JUnit4.class). And of course your java test file is under app/src/test/java/your.package.name directory.

Else if (!!) we want to write some Android Instrumented Unit Test we should put our test java files in app/src/androidTest/java/your.package.name directory and use annotation like @RunWith(AndroidJUnit4.class)