Index: trunk/test/unit/org/openstreetmap/josm/tools/date/DateUtilsTest.java
===================================================================
--- trunk/test/unit/org/openstreetmap/josm/tools/date/DateUtilsTest.java	(revision 17094)
+++ trunk/test/unit/org/openstreetmap/josm/tools/date/DateUtilsTest.java	(revision 17104)
@@ -10,6 +10,9 @@
 import java.text.DateFormat;
 import java.util.Date;
+import java.util.Random;
 import java.util.TimeZone;
-
+import java.util.concurrent.ForkJoinPool;
+
+import org.junit.Ignore;
 import org.junit.Rule;
 import org.junit.Test;
@@ -192,6 +195,15 @@
 
         // Local time
-        TimeZone.setDefault(TimeZone.getTimeZone("Europe/Berlin"));
+        setTimeZone(TimeZone.getTimeZone("Europe/Berlin"));
         assertEquals(1459688400000L, DateUtils.tsFromString("03-APR-16 15:00:00"));
+    }
+
+    @Test
+    @Ignore("slow; use for thread safety testing")
+    public void testTsFromString800k() throws Exception {
+        new ForkJoinPool(64).submit(() -> new Random()
+                .longs(800_000)
+                .parallel()
+                .forEach(ignore -> testTsFromString())).get();
     }