@Test
public void testSingleFieldConstraintPredicate() {

    Map<InterpolationVariable, Integer> variableMap = new HashMap<>();
    RuleModelVisitor visitor = new RuleModelVisitor(variableMap);
    SingleFieldConstraint singleFieldConstraint = new SingleFieldConstraint();
    singleFieldConstraint.setConstraintValueType(BaseSingleFieldConstraint.TYPE_PREDICATE);
    singleFieldConstraint.setValue("(age != null) == \"@{param1}\"");
    visitor.visit(singleFieldConstraint);
    assertEquals(1, variableMap.keySet().size());
    InterpolationVariable interpolationVariable = variableMap.keySet().iterator().next();
    assertEquals("param1", interpolationVariable.getVarName());
    assertEquals("Object", interpolationVariable.getDataType());
    assertNull(interpolationVariable.getFactField());
    assertNull(interpolationVariable.getOperator());
}