Fix token adapter instrumented tests

Upgrade Mockito from 2.23.0 to 2.24.0 to avoid the following issue:
org.mockito.exceptions.base.MockitoException: Mockito cannot mock this class:
class android.content.Context.  Underlying exception :
java.lang.IllegalArgumentException: On Android P, a class injection can only be
applied to BaseDexClassLoader:
net.bytebuddy.dynamic.loading.MultipleParentClassLoader@23f7dce

Looking at Mockito 2.x release notes:
https://github.com/mockito/mockito/blob/release/2.x/doc/release-notes/official.md

- Previous issue may have been fixed in later 2.23.18 published on now
  unavailable Mockito Bintray repository. Consequently, move to 2.24.0 release
available on Maven Central.
- It seems that from 2.23.13 and androidx.test support added, tests are now
  launched in a dedicated instrumentation thread that does not prepare an
Android Looper. But as Adapter class will instatiate an Android Handler, even
if not needed for the tests, the following error is encountered:
java.lang.RuntimeException: Can't create handler inside thread Thread[Instr:
androidx.test.runner.AndroidJUnitRunner,5,main] that has not called
Looper.prepare()
Consequently, force the Looper to be prepared once before tests.

mobile/build.gradle

@@ -47,8 +47,8 @@ dependencies {
     implementation 'androidx.appcompat:appcompat:1.4.1'
     implementation 'androidx.constraintlayout:constraintlayout:2.1.4'
     testImplementation 'junit:junit:4.12'
-    testImplementation 'org.mockito:mockito-core:2.23.0'
-    androidTestImplementation 'org.mockito:mockito-android:2.23.0'
+    testImplementation 'org.mockito:mockito-core:2.24.0'
+    androidTestImplementation 'org.mockito:mockito-android:2.24.0'
     androidTestImplementation 'androidx.test.ext:junit:1.1.3'
     androidTestImplementation 'com.android.support.test:runner:1.0.2'
     androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'

mobile/src/androidTest/java/org/fedorahosted/freeotp/TokenAdapterTest.java

@@ -2,6 +2,7 @@
 
 import android.content.Context;
 import android.content.SharedPreferences;
+import android.os.Looper;
 import android.util.Log;
 import android.util.Pair;
 
@@ -12,6 +13,7 @@
 import org.json.JSONArray;
 import org.json.JSONException;
 import org.junit.Before;
+import org.junit.BeforeClass;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.Mock;
@@ -55,6 +57,14 @@ private int getSize() {
     public TokenAdapterTest() throws Token.InvalidUriException {
     }
 
+    @BeforeClass
+    public static void setupOnce() {
+        // Instrumented tests are launched in a dedicated instrumentation thread that does not prepare an Android Looper.
+        // But it is mandatory here as Adapter will instantiate an Android Handler.
+        if (Looper.myLooper() == null)
+            Looper.prepare();
+    }
+
     @Before
     public void setup() {
         when(mockContext.getSharedPreferences(anyString(), anyInt()))