Index: trunk/test/unit/org/openstreetmap/josm/tools/TerritoriesTest.java
===================================================================
--- trunk/test/unit/org/openstreetmap/josm/tools/TerritoriesTest.java	(revision 15951)
+++ trunk/test/unit/org/openstreetmap/josm/tools/TerritoriesTest.java	(revision 15952)
@@ -2,8 +2,17 @@
 package org.openstreetmap.josm.tools;
 
+import static java.util.Collections.singleton;
 import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+import java.util.TreeMap;
 
 import org.junit.Rule;
 import org.junit.Test;
+import org.openstreetmap.josm.TestUtils;
 import org.openstreetmap.josm.data.coor.LatLon;
 import org.openstreetmap.josm.testutils.JOSMTestRules;
@@ -45,3 +54,40 @@
         }
     }
+
+    /**
+     * Test of {@link Territories#initializeExternalData} - nominal case
+     */
+    @Test
+    public void testTaginfoGeofabrik_nominal() {
+        Map<String, TaginfoRegionalInstance> cache = new TreeMap<>();
+        Territories.initializeExternalData(cache, "foo", TestUtils.getTestDataRoot() + "/taginfo/geofabrik-index-v1-nogeom.json");
+        assertEquals(5, cache.size());
+        checkTaginfoInstance(cache.get("AF"), singleton("AF"), "https://taginfo.geofabrik.de/asia/afghanistan/");
+        checkTaginfoInstance(cache.get("AL"), singleton("AL"), "https://taginfo.geofabrik.de/europe/albania/");
+        checkTaginfoInstance(cache.get("CA-AB"), singleton("CA-AB"), "https://taginfo.geofabrik.de/north-america/canada/alberta/");
+        Set<String> israelAndPalestine = new HashSet<>(Arrays.asList("PS", "IL"));
+        checkTaginfoInstance(cache.get("PS"), israelAndPalestine, "https://taginfo.geofabrik.de/asia/israel-and-palestine/");
+        checkTaginfoInstance(cache.get("IL"), israelAndPalestine, "https://taginfo.geofabrik.de/asia/israel-and-palestine/");
+    }
+
+    private static void checkTaginfoInstance(TaginfoRegionalInstance instance, Set<String> expectedIsoCodes, String expectedUrl) {
+        assertEquals(expectedIsoCodes, instance.getIsoCodes());
+        assertEquals("foo", instance.getSuffix());
+        assertEquals(expectedUrl, instance.getUrl());
+    }
+
+    /**
+     * Test of {@link Territories#initializeExternalData} - broken contents
+     */
+    @Test
+    public void testTaginfoGeofabrik_broken() {
+        Map<String, TaginfoRegionalInstance> cache = new TreeMap<>();
+        Logging.clearLastErrorAndWarnings();
+        Territories.initializeExternalData(cache, "foo", TestUtils.getTestDataRoot() + "taginfo/geofabrik-index-v1-nogeom-broken.json");
+        assertTrue(cache.isEmpty());
+        assertEquals("W: Failed to parse external taginfo data at test/data/taginfo/geofabrik-index-v1-nogeom-broken.json: " +
+                "Invalid token=EOF at (line no=3, column no=49, offset=97). Expected tokens are: " +
+                "[CURLYOPEN, SQUAREOPEN, STRING, NUMBER, TRUE, FALSE, NULL, SQUARECLOSE]",
+                Logging.getLastErrorAndWarnings().get(0));
+    }
 }