See #21605: Add tabs to ImageViewerDialog for use with different image layers

This fixes a broken test. This occurred because this was the only location where
GeoImageLayer was initialized with a `null` image list. We also needed to add
`main()` from JOSMTestRules due to initializing the image viewer in the
constructor, if no image viewer was already initialized.

git-svn-id: https://josm.openstreetmap.de/svn/trunk@18614 0c6e7542-c601-0410-84e7-c038aed88b3b

Author: taylor.smock

test/unit/org/openstreetmap/josm/gui/layer/geoimage/GeoImageLayerTest.java

@@ -3,8 +3,12 @@
 
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
+import java.util.Collections;
+
+import org.junit.jupiter.api.extension.RegisterExtension;
 import org.openstreetmap.josm.data.osm.DataSet;
 import org.openstreetmap.josm.gui.layer.OsmDataLayer;
+import org.openstreetmap.josm.testutils.JOSMTestRules;
 import org.openstreetmap.josm.testutils.annotations.BasicPreferences;
 
 import org.junit.jupiter.api.Test;
@@ -15,12 +19,16 @@
 // Basic preferences are needed for OSM primitives
 @BasicPreferences
 class GeoImageLayerTest {
+    @RegisterExtension
+    static JOSMTestRules josmTestRules = new JOSMTestRules().main();
 
     /**
      * Test that {@link GeoImageLayer#mergeFrom} throws IAE for invalid arguments
      */
     @Test
     void testMergeFromIAE() {
-        assertThrows(IllegalArgumentException.class, () -> new GeoImageLayer(null, null).mergeFrom(new OsmDataLayer(new DataSet(), "", null)));
+        GeoImageLayer geoImageLayer = new GeoImageLayer(Collections.emptyList(), null);
+        OsmDataLayer osmDataLayer = new OsmDataLayer(new DataSet(), "", null);
+        assertThrows(IllegalArgumentException.class, () -> geoImageLayer.mergeFrom(osmDataLayer));
     }
 }