1 files changed, 37 insertions, 4 deletions
diff --git a/app/src/main/java/se/leap/bitmaskclient/base/utils/FileHelper.java b/app/src/main/java/se/leap/bitmaskclient/base/utils/FileHelper.java
index eb1c255c..f1d86876 100644
--- a/app/src/main/java/se/leap/bitmaskclient/base/utils/FileHelper.java
+++ b/app/src/main/java/se/leap/bitmaskclient/base/utils/FileHelper.java
@@ -2,6 +2,8 @@ package se.leap.bitmaskclient.base.utils;
 
 import android.content.Context;
 
+import androidx.annotation.VisibleForTesting;
+
 import java.io.BufferedReader;
 import java.io.File;
 import java.io.FileWriter;
@@ -9,19 +11,50 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
 
+import de.blinkt.openvpn.core.NativeUtils;
+
 /**
  * Created by cyberta on 18.03.18.
  */
 
 public class FileHelper {
+
+    public interface FileHelperInterface {
+        File createFile(File dir, String fileName);
+        void persistFile(File file, String content) throws IOException;
+    }
+
+    public static class DefaultFileHelper implements FileHelperInterface {
+        @Override
+        public File createFile(File dir, String fileName) {
+            return new File(dir, fileName);
+        }
+
+        @Override
+        public void persistFile(File file, String content) throws IOException {
+            FileWriter writer = new FileWriter(file);
+            writer.write(content);
+            writer.close();
+        }
+    }
+
+    private static FileHelperInterface instance = new DefaultFileHelper();
+
+    @VisibleForTesting
+    public FileHelper(FileHelperInterface helperInterface) {
+        if (!NativeUtils.isUnitTest()) {
+            throw new IllegalStateException("FileHelper injected with FileHelperInterface outside of an unit test");
+        }
+
+        instance = helperInterface;
+    }
+
     public static File createFile(File dir, String fileName) {
-        return new File(dir, fileName);
+        return instance.createFile(dir, fileName);
     }
 
     public static void persistFile(File file, String content) throws IOException {
-        FileWriter writer = new FileWriter(file);
-        writer.write(content);
-        writer.close();
+        instance.persistFile(file, content);
     }
 
     public static String readPublicKey(Context context) {