Issue#67 Extract runOnUIAwaitOnCurrent into separate module

test-util-android/src/main/AndroidManifest.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="org.fnives.test.showcase.android.testutil">
+
+</manifest>

test-util-android/src/main/java/org/fnives/test/showcase/android/testutil/synchronization/doBlockinglyOnMainThread.kt

@@ -0,0 +1,24 @@
+package org.fnives.test.showcase.android.testutil.synchronization
+
+import android.os.Handler
+import android.os.Looper
+import kotlinx.coroutines.CompletableDeferred
+import kotlinx.coroutines.runBlocking
+
+/**
+ * Runs the given action on the MainThread and blocks currentThread, until it is completed.
+ *
+ * It is safe to call this from the MainThread.
+ */
+fun runOnUIAwaitOnCurrent(action: () -> Unit) {
+    if (Looper.myLooper() === Looper.getMainLooper()) {
+        action()
+    } else {
+        val deferred = CompletableDeferred<Unit>()
+        Handler(Looper.getMainLooper()).post {
+            action()
+            deferred.complete(Unit)
+        }
+        runBlocking { deferred.await() }
+    }
+}