Credit: https://github.com/spongebobrf/android-retrofit-test-examples

[TESTING] Read json file from assets (for testing-mock)

package za.co.riggaroo.retrofittestexample;

import android.content.Context;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;

/**
 * @author rebeccafranks
 * @since 15/10/24.
 */
public class RestServiceTestHelper {

    public static String convertStreamToString(InputStream is) throws Exception {
        BufferedReader reader = new BufferedReader(new InputStreamReader(is));
        StringBuilder sb = new StringBuilder();
        String line;
        while ((line = reader.readLine()) != null) {
            sb.append(line).append("\n");
        }
        reader.close();
        return sb.toString();
    }

    public static String getStringFromFile(Context context, String filePath) throws Exception {
        final InputStream stream = context.getResources().getAssets().open(filePath);

        String ret = convertStreamToString(stream);
        //Make sure you close all streams.
        stream.close();
        return ret;
    }
}