private Tensor evaluate(String expr, Tensor x, Tensor y, Tensor z) throws ParseException {
        Context context = new MapContext(DoubleValue.NaN);
        if (x != null) context.put("x", new TensorValue(x));
        if (y != null) context.put("y", new TensorValue(y));
        if (z != null) context.put("z", new TensorValue(z));
        return new RankingExpression(expr).evaluate(context).asTensor();
    }
Unit tests for ONNX operators. The number on the test reflects the minimum
opset number for the operations tested.

@author lesters
model-integration/src/test/java/ai/vespa/rankingexpression/importer/onnx/OnnxOperationsTestCase.java