Add DrawableUtilTests for testing overlaying icons

Signed-off-by: Alper Ozturk <alperozturk@lions-macbook.local>
Signed-off-by: alperozturk <alper_ozturk@proton.me>

app/src/androidTest/java/com/owncloud/android/utils/DrawableUtilTests.kt

@@ -0,0 +1,42 @@
+package com.owncloud.android.utils
+
+import android.content.Context
+import android.graphics.Bitmap
+import android.graphics.drawable.BitmapDrawable
+import androidx.test.platform.app.InstrumentationRegistry
+import org.junit.After
+import org.junit.Assert.fail
+import org.junit.Before
+import org.junit.Test
+
+class DrawableUtilTests {
+
+    private var sut: DrawableUtil? = null
+    private var context: Context? = null
+
+    @Before
+    fun setUp() {
+        sut = DrawableUtil()
+        context = InstrumentationRegistry.getInstrumentation().context
+    }
+
+    @Test
+    fun testAddDrawableAsOverlayWhenGivenValidDrawablesShouldContainTwoDrawable() {
+        val bitmap: Bitmap = Bitmap.createBitmap(10, 10, Bitmap.Config.ARGB_8888)
+        val drawable = BitmapDrawable(context?.resources, bitmap)
+
+        val layerDrawable = sut?.addDrawableAsOverlay(drawable, drawable)
+
+        if (layerDrawable == null) {
+            fail("Layer drawable expected to be not null")
+        }
+
+        assert(layerDrawable?.numberOfLayers == 2)
+    }
+
+    @After
+    fun destroy() {
+        sut = null
+        context = null
+    }
+}