Function exp = ff.function("octagonalenvelope", ff.property("geom"));
SimpleFeatureIterator iter = featureCollection.features();
while (iter.hasNext()) {
SimpleFeature feature = iter.next();
Geometry geom = (Geometry) feature.getDefaultGeometry();
Geometry octagonalEnvelope = new OctagonalEnvelope(geom).toGeometry(geom.getFactory());
Object value = exp.evaluate(feature);
assertTrue(value instanceof Polygon);
assertTrue(octagonalEnvelope.equalsExact((Geometry) value, 0.1));
}
iter.close();