Fixed ChartFragment tests.

Initialization of looper was missing.

src/androidTest/java/de/dennisguse/opentracks/fragments/ChartFragmentTest.java

@@ -17,12 +17,15 @@
 package de.dennisguse.opentracks.fragments;
 
 import android.location.Location;
+import android.os.Looper;
 
 import androidx.test.core.app.ApplicationProvider;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
 
+import org.junit.AfterClass;
 import org.junit.Assert;
 import org.junit.Before;
+import org.junit.BeforeClass;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 
@@ -44,6 +47,17 @@ public class ChartFragmentTest {
 
     private ChartFragment chartFragment;
 
+    @BeforeClass
+    public static void preSetUp() {
+        // Prepare looper for Android's message queue
+        if (Looper.myLooper() == null) Looper.prepare();
+    }
+
+    @AfterClass
+    public static void finalTearDown() {
+        if (Looper.myLooper() != null) Looper.myLooper().quit();
+    }
+
     @Before
     public void setUp() {
         boolean chartByDistance = false;