private void assertDecodeFails(TensorType type, String format, String msg) {
        try {
            Tensor decoded = JsonFormat.decode(type, format.getBytes(StandardCharsets.UTF_8));
            fail("Did not get exception as expected, decoded as: " + decoded);
        } catch (IllegalArgumentException e) {
            assertEquals(msg, e.getMessage());
        }
    }
All cell types are rendered as double.
vespajlib/src/test/java/com/yahoo/tensor/serialization/JsonFormatTestCase.java