Robolectric Gradle test runner so that Config annotation isn't required on each of your test classes.

CustomRobolectricTestRunner.java

public class CustomRobolectricTestRunner extends RobolectricGradleTestRunner {

    private static final int MAX_SDK_LEVEL = 21;
    
    public CustomRobolectricTestRunner(Class<?> testClass) throws InitializationError {
        super(testClass);
    }

    @Override
    public Config getConfig(Method method) {
        Config config = super.getConfig(method);

        config = new Config.Implementation(
                ensureSdkLevels(config.sdk()),
                config.manifest(),
                config.qualifiers(),
                config.packageName(),
                config.resourceDir(),
                config.assetDir(),
                config.shadows(),
                config.application(),
                config.libraries(),
                ensureBuildConfig(config.constants()));

        return config;
    }

    private Class<?> ensureBuildConfig(Class<?> constants) {
        if (constants == Void.class) return BuildConfig.class;
        return constants;
    }

    private int[] ensureSdkLevels(int[] sdkLevels) {
        int numberSdks = sdkLevels.length;
        int[] sdks = new int[numberSdks];
        for (int i = 0; i < numberSdks; i++) {
            int sdk = sdks[i];
            if (sdk > MAX_SDK_LEVEL || sdk <= 0) {
                sdks[i] = MAX_SDK_LEVEL;
            } else {
                sdks[i] = sdk;
            }
        }
        return sdks;
    }

}