Test & I18N for checkSanity.

core/src/main/java/hudson/scheduler/CronTab.java

@@ -420,8 +420,7 @@ public final class CronTab {
                     // this rank has a sparse entry.
                     // if we have a sparse rank, one of them better be the left-most.
                     if(i>0)
-                        return "Do you really mean \"every minute\" when you say \""+spec+"\"? "+
-                                "Perhaps you meant \"0 "+spec.substring(spec.indexOf(' ')+1)+"\"";
+                        return Messages.CronTab_do_you_really_mean_every_minute_when_you(spec, "0 " + spec.substring(spec.indexOf(' ')+1));
                     // once we find a sparse rank, upper ranks don't matter
                     return null;
                 }

core/src/main/resources/hudson/scheduler/Messages.properties

@@ -23,4 +23,5 @@
 BaseParser.StartEndReversed=You mean {0}-{1}?
 BaseParser.MustBePositive=step must be positive, but found {0}
 BaseParser.OutOfRange={0} is an invalid value. Must be within {1} and {2}
-CronTabList.InvalidInput=Invalid input: "{0}": {1}
\ No newline at end of file
+CronTab.do_you_really_mean_every_minute_when_you=Do you really mean "every minute" when you say "{0}"? Perhaps you meant "{1}"
+CronTabList.InvalidInput=Invalid input: "{0}": {1}

core/src/test/java/hudson/scheduler/CronTabTest.java

@@ -178,6 +178,17 @@ public class CronTabTest {
         compare(answer,x.floor(c));
     }
 
+    @Test public void checkSanity() throws Exception {
+        assertEquals(Messages.CronTab_do_you_really_mean_every_minute_when_you("* * * * *", "0 * * * *"), new CronTab("* * * * *").checkSanity());
+        assertEquals(null, new CronTab("0 * * * *").checkSanity());
+        assertEquals(null, new CronTab("0 3 * * *").checkSanity());
+        assertEquals(null, new CronTab("H H(0-2) * * *", Hash.from("stuff")).checkSanity());
+        assertEquals(Messages.CronTab_do_you_really_mean_every_minute_when_you("* 0 * * *", "0 0 * * *"), new CronTab("* 0 * * *").checkSanity());
+        assertEquals(Messages.CronTab_do_you_really_mean_every_minute_when_you("* 6,18 * * *", "0 6,18 * * *"), new CronTab("* 6,18 * * *").checkSanity());
+        // dubious; could be improved:
+        assertEquals(Messages.CronTab_do_you_really_mean_every_minute_when_you("* * 3 * *", "0 * 3 * *"), new CronTab("* * 3 * *").checkSanity());
+    }
+
     /**
      * Humans can't easily see difference in two {@link Calendar}s, do help the diagnosis by using {@link DateFormat}. 
      */