@Test
    public void testMissingFieldsMapInUpdate() {
        try {
            String jsonData = """
                              [
                                {
                                  "update": "id:unittest:smoke::whee"
                                }
                              ]""";

            new JsonReader(types, jsonToInputStream(jsonData), parserFactory).next();
            fail("Expected exception");
        }
        catch (IllegalArgumentException e) {
            assertEquals("Update of document id:unittest:smoke::whee is missing a 'fields' map", e.getMessage());
        }
    }
Basic test of JSON streams to Vespa document instances.

@author Steinar Knutsen
@author bratseth
document/src/test/java/com/yahoo/document/json/JsonReaderTestCase.java