Index: /trunk/src/org/openstreetmap/josm/data/imagery/vectortile/mapbox/style/MapboxVectorStyle.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/imagery/vectortile/mapbox/style/MapboxVectorStyle.java	(revision 17989)
+++ /trunk/src/org/openstreetmap/josm/data/imagery/vectortile/mapbox/style/MapboxVectorStyle.java	(revision 17990)
@@ -282,3 +282,11 @@
         return Objects.hash(this.name, this.version, this.glyphUrl, this.spriteUrl, this.sources);
     }
+
+    @Override
+    public String toString() {
+        return "MapboxVectorStyle [version=" + version + ", " + (name != null ? "name=" + name + ", " : "")
+                + (spriteUrl != null ? "spriteUrl=" + spriteUrl + ", " : "")
+                + (glyphUrl != null ? "glyphUrl=" + glyphUrl + ", " : "")
+                + (sources != null ? "sources=" + sources : "") + "]";
+    }
 }
Index: /trunk/test/unit/org/openstreetmap/josm/data/imagery/vectortile/mapbox/style/MapboxVectorStyleTest.java
===================================================================
--- /trunk/test/unit/org/openstreetmap/josm/data/imagery/vectortile/mapbox/style/MapboxVectorStyleTest.java	(revision 17989)
+++ /trunk/test/unit/org/openstreetmap/josm/data/imagery/vectortile/mapbox/style/MapboxVectorStyleTest.java	(revision 17990)
@@ -238,5 +238,5 @@
         final String file = "file:/" + TestUtils.getTestDataRoot() + "/mapillary.json";
         final MapboxVectorStyle style = MapboxVectorStyle.getMapboxVectorStyle(file);
-        assertNotNull(style);
+        assertNotNull(style, file);
         // There are three "sources" in the mapillary.json file
         assertEquals(3, style.getSources().size());
@@ -244,11 +244,11 @@
           .filter(source -> "mapillary-source".equals(source.getKey().getName())).map(
             Map.Entry::getValue).findAny().orElse(null);
-        assertNotNull(mapillarySource);
+        assertNotNull(mapillarySource, style.toString());
         mapillarySource.getStyleSources().forEach(StyleSource::loadStyleSource);
         assertEquals(1, mapillarySource.getStyleSources().size());
         final MapCSSStyleSource mapillaryCssSource = (MapCSSStyleSource) mapillarySource.getStyleSources().get(0);
-        assertTrue(mapillaryCssSource.getErrors().isEmpty());
+        assertTrue(mapillaryCssSource.getErrors().isEmpty(), mapillaryCssSource.getErrors().toString());
         final MapCSSRule mapillaryOverview = getRule(mapillaryCssSource, "node", "mapillary-overview");
-        assertNotNull(mapillaryOverview);
+        assertNotNull(mapillaryOverview, mapillaryCssSource.toString());
         assertInInstructions(mapillaryOverview.declaration.instructions, "symbol-shape", new Keyword("circle"));
         assertInInstructions(mapillaryOverview.declaration.instructions, "symbol-fill-color", ColorHelper.html2color("#05CB63"));