ShadowFirebaseApp.java

package com.lastminutedevice.gists;

import android.content.Context;

import androidx.test.platform.app.InstrumentationRegistry;

import com.google.firebase.FirebaseApp;

import org.robolectric.annotation.Implementation;
import org.robolectric.annotation.Implements;
import org.robolectric.shadow.api.Shadow;
import org.robolectric.util.ReflectionHelpers;

/**
 * On a real running app, the FirebaseInitProvider would have initialized FirebaseApp
 * on application start. Robolectic doesn't make that happen.
 * <p>
 * This gets around that problem by having it initialize itself if needed.
 */
@Implements(FirebaseApp.class)
public class ShadowFirebaseApp {

    @Implementation
    public static FirebaseApp getInstance() {

        try {
            return Shadow.directlyOn(FirebaseApp.class, "getInstance");
        } catch (IllegalStateException exception) {
            // It hasn't been initialized.
        }

        Context targetContext = InstrumentationRegistry
                .getInstrumentation()
                .getTargetContext();
        ReflectionHelpers.ClassParameter<Context> contextClassParameter = ReflectionHelpers
                .ClassParameter
                .from(Context.class, targetContext);

        Shadow.directlyOn(FirebaseApp.class, "initializeApp", contextClassParameter);

        return Shadow.directlyOn(FirebaseApp.class, "getInstance");
    }
}