histogram: test getBinSpanLabelRound for zero gaps

Author: antoinerg

test/jasmine/tests/histogram_test.js

@@ -1365,6 +1365,10 @@ describe('getBinSpanLabelRound', function() {
         _test(500, 500, [4500, 9500, 14500], false, [5000, 9000, 10000, 14000]);
     });
 
+    it('works when gaps are zero', function() {
+        _test(0, 0, [-0.5, 4.5, 9.5], false, [-0.5, 4.5, 4.5, 9.5]);
+    });
+
     var jan17 = Date.UTC(2017, 0, 1);
     var feb17 = Date.UTC(2017, 1, 1);
     var mar17 = Date.UTC(2017, 2, 1);