pivotSpec.addFilter("has_boris", BooleanComparison.EQUALS, true);
Assert.assertEquals(1, pivotSpec.getFilters().size());
for (PivotFilter pf : pivotSpec.getFilters()) {
Assert.assertTrue(pf instanceof BooleanPivotFilter);
JsonElement obj = pf.toJson();
Assert.assertTrue(obj instanceof JsonObject);
JsonObject o = (JsonObject)obj;
Assert.assertTrue(o.has("fieldName"));
Assert.assertEquals(new JsonPrimitive("has_boris"), o.get("fieldName"));