In a previous blog post, I talked about how Gradle allows us to add string resources that can be changed depending on your build configuration, like so:

android {
 buildTypes {
 debug {
 resValue "string", "google_maps_android_api_key", "abcdefghijklm123"
 }
 release {
 resValue "string", "google_maps_android_api_key", "nopqrstuvwxyz456"
 }
 }
}

This generates a string resource that we can then use in our code:

String mapsKey = getString(R.string.google_maps_android_api_key);

However, if you use the Robolectric testing framework (version 2.4) and this line is executed during a test, then you will get the following error in your LogCat:

android.content.res.Resources$NotFoundException: String resource ID #0x7f0c004e

Since this string resource is only generated during a Gradle build and not during Robolectric test execution, Robolectric is not able to find this string resource and this exception is thrown.

The solution

If we attempt to put a dummy string in our strings.xml file…

<string name="google_maps_android_api_key">dummy maps key</string>

…so that this exception doesn’t happen, Robolectric tests will run just fine, but when you build your project it will complain about duplicate resources, as Gradle is trying to generate a resource of the same name.

The solution is to create a shadow resource for this generated string. Create the following class in your test package:

import android.content.res.Resources;
import org.robolectric.annotation.Implements;
import org.robolectric.shadows.ShadowResources;

/**
 * This class is used to generate Android resources that are otherwise
 * not present during Robolectric tests, such as string resources generated
 * by Gradle with resValue.
 */
@Implements(Resources.class)
public class CustomShadowResources extends ShadowResources {
 @Override
 public CharSequence getText(int id) throws Resources.NotFoundException {
 if (id == R.string.google_maps_android_api_key) return "dummy maps key";

 return super.getText(id);
 }
}

In your test class that is throwing the exception, add a “shadows” annotation parameter to your “Config” annotation that points to your new shadow class:

@Config(
 shadows = CustomShadowResources.class,
 ...
)
@RunWith(RobolectricTestRunner.class)
public class SomeActivityTest {
 ...
}

How it works

The shadow class defines what to do when Robolectric comes across certain types of resources. In this case, when your code tries to access the generated string resource…

String mapsKey = getString(R.string.google_maps_android_api_key);

…Robolectric will use the shadow class’s overridden method to return a dummy string when testing execution comes across use of this string resource, and the Resources$NotFoundException will no longer be thrown.