static Tensor mmTensor() {
        return Tensor.from("tensor(x{},y{}):{ {x:a,y:0}:1.0, {x:b,y:1}:2.0 }");
    }
Functional testing of {@link JsonRenderer}.

@author Steinar Knutsen
@author bratseth
container-search/src/test/java/com/yahoo/search/rendering/JsonRendererTestCase.java