How to access files from assets folder during tests execution?

How to access files from assets folder during unit tests execution? My project is build using Gradle, I use Robolectric to run tests. It seems like gradle is being recognizing the assets:

This is how I'm struggling to read the file:

public String readFileFromAssets(String fileName) throws IOException {
    InputStream stream = getClass().getClassLoader().getResourceAsStream("assets/" + fileName);
    Preconditions.checkNotNull(stream, "Stream is null");
    BufferedReader reader = new BufferedReader(new InputStreamReader(stream, "UTF-8"));
    return IOUtils.toString(reader);
}

But stream is always null. I tried it many different ways, i.e. defined path to a file using different approaches.

Thank you very much in advance.

Basically you have to use Context to read assets. You can not load assets with ClassLoader since it is not in a classpath. I am not sure how you run Robolectric test cases. Here are how I can achieve in both Android studio and gralde command.

I added separate app-unit-test module to run Robolectric test cases in app project. With proper build configuration and custom RobolectricTestRunner, following test case will pass.

@Config
@RunWith(MyRobolectricTestRunner.class)
public class ReadAssetsTest {

    @Test
    public void test_ToReadAssetsFileInAndroidTestContext() throws IOException {

        ShadowApplication application = Robolectric.getShadowApplication();
        Assert.assertNotNull(application);
        InputStream input = application.getAssets().open("b.xml");
        Assert.assertNotNull(input);
    }

}

app-unit-test/build.gradle

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:0.14.1'
    }
}

apply plugin: 'java'
evaluationDependsOn(':app')

sourceCompatibility = JavaVersion.VERSION_1_7
targetCompatibility = JavaVersion.VERSION_1_7

repositories {
    maven { url "$System.env.ANDROID_HOME/extras/android/m2repository" } // Fix 'com.android.support:*' package not found issue
    mavenLocal()
    mavenCentral()
    jcenter()
}

dependencies {
    testCompile 'junit:junit:4.8.2'
    testCompile('org.robolectric:robolectric:2.4') {
        exclude module: 'classworlds'
        exclude module: 'commons-logging'
        exclude module: 'httpclient'
        exclude module: 'maven-artifact'
        exclude module: 'maven-artifact-manager'
        exclude module: 'maven-error-diagnostics'
        exclude module: 'maven-model'
        exclude module: 'maven-project'
        exclude module: 'maven-settings'
        exclude module: 'plexus-container-default'
        exclude module: 'plexus-interpolation'
        exclude module: 'plexus-utils'
        exclude module: 'wagon-file'
        exclude module: 'wagon-http-lightweight'
        exclude module: 'wagon-provider-api'
        exclude group: 'com.android.support', module: 'support-v4'
    }
    testCompile('com.squareup:fest-android:1.0.+') {
        exclude group: 'com.android.support', module: 'support-v4'
    }
    testCompile 'org.mockito:mockito-core:1.10.10'
    def appModule = project(':app')
    testCompile(appModule) {
        exclude group: 'com.google.android'
        exclude module: 'dexmaker-mockito'
    }
    testCompile appModule.android.applicationVariants.toList().first().javaCompile.classpath
    testCompile appModule.android.applicationVariants.toList().first().javaCompile.outputs.files
    testCompile 'com.google.android:android:4.1.1.4'
    /* FIXME : prevent Stub! error
        testCompile files(appModule.plugins.findPlugin("com.android.application").getBootClasspath())
        */
    compile project(':app')
}

Add custom RobolectricTestRunner to adjust file paths. Look at the assets path.

public class MyRobolectricTestRunner extends RobolectricTestRunner {

    private static final String APP_MODULE_NAME = "app";

    /**
     * Creates a runner to run {@code testClass}. Looks in your working directory for your AndroidManifest.xml file
     * and res directory by default. Use the {@link org.robolectric.annotation.Config} annotation to configure.
     *
     * @param testClass the test class to be run
     * @throws org.junit.runners.model.InitializationError if junit says so
     */
    public MyRobolectricTestRunner(Class<?> testClass) throws InitializationError {
        super(testClass);
        System.out.println("testclass="+testClass);
    }

    @Override
    protected AndroidManifest getAppManifest(Config config) {

        String userDir = System.getProperty("user.dir", "./");
        File current = new File(userDir);
        String prefix;
        if (new File(current, APP_MODULE_NAME).exists()) {
            System.out.println("Probably running on AndroidStudio");
            prefix = "./" + APP_MODULE_NAME;
        }
        else if (new File(current.getParentFile(), APP_MODULE_NAME).exists()) {
            System.out.println("Probably running on Console");
            prefix = "../" + APP_MODULE_NAME;
        }
        else {
            throw new IllegalStateException("Could not find app module, app module should be \"app\" directory in the project.");
        }
        System.setProperty("android.manifest", prefix + "/src/main/AndroidManifest.xml");
        System.setProperty("android.resources", prefix + "/src/main/res");
        System.setProperty("android.assets", prefix + "/src/androidTest/assets");

        return super.getAppManifest(config);
    }

}

I followed this blog to do it.

• http://blog.blundellapps.com/android-gradle-app-with-robolectric-junit-tests/
• http://blog.blundellapps.com/how-to-run-robolectric-junit-tests-in-android-studio/

Full example codes are here.