@Test
    public void testPartialUpdateWithMultipleFieldsAssign() {
        var tester = new PartialUpdateTester();

        DocumentUpdate input = new DocumentUpdate(tester.inputType, "id:ns:test::");
        input.addFieldUpdate(FieldUpdate.createAssign(tester.inputType.getField("stringField"), new StringFieldValue("newValue")));

        DocumentUpdate output = tester.process(input);
        assertEquals(1, output.fieldUpdates().size());
        var fieldUpdate = output.fieldUpdates().iterator().next();
        assertEquals(1, fieldUpdate.getValueUpdates().size());
        var valueUpdate = fieldUpdate.getValueUpdates().iterator().next();
        assertTrue(valueUpdate instanceof AssignValueUpdate);
        assertEquals("newValue", valueUpdate.getValue().getWrappedValue());
    }
Test sending assign of 1 field only, when needing 2.
TODO Vespa 9: This is allowed, but shouldn't be.
docprocs/src/test/java/com/yahoo/docprocs/indexing/IndexingProcessorTestCase.java