Example:

public void conditionEvaluationExtensionPoint(String fieldCode, byte comparisonResult, String comparisonError,
                                              String expectedResult) throws Exception {
    final String LEFT = "\"left expression\"";
    final String _OPERATOR = "<>";
    final String RIGHT = "\"right expression\"";

    DocumentBuilder builder = new DocumentBuilder();

    // Field codes that we use in this example:
    // 1.   " IF %s %s %s \"true argument\" \"false argument\" ".
    // 2.   " COMPARE %s %s %s ".
    Field field = builder.insertField(String.format(fieldCode, LEFT, _OPERATOR, RIGHT), null);

    // If the "comparisonResult" is undefined, we create "ComparisonEvaluationResult" with string, instead of bool.
    ComparisonEvaluationResult result = comparisonResult != -1
            ? new ComparisonEvaluationResult(comparisonResult == 1)
            : comparisonError != null ? new ComparisonEvaluationResult(comparisonError) : null;

    ComparisonExpressionEvaluator evaluator = new ComparisonExpressionEvaluator(result);
    builder.getDocument().getFieldOptions().setComparisonExpressionEvaluator(evaluator);

    builder.getDocument().updateFields();

    Assert.assertEquals(expectedResult, field.getResult());
    evaluator.assertInvocationsCount(1).assertInvocationArguments(0, LEFT, _OPERATOR, RIGHT);
}

public static Object[][] conditionEvaluationExtensionPointDataProvider() {
    return new Object[][]
            {
                    {" IF %s %s %s \"true argument\" \"false argument\" ", (byte) 1, null, "true argument"},
                    {" IF %s %s %s \"true argument\" \"false argument\" ", (byte) 0, null, "false argument"},
                    {" IF %s %s %s \"true argument\" \"false argument\" ", (byte) -1, "Custom Error", "Custom Error"},
                    {" IF %s %s %s \"true argument\" \"false argument\" ", (byte) -1, null, "true argument"},
                    {" COMPARE %s %s %s ", (byte) 1, null, "1"},
                    {" COMPARE %s %s %s ", (byte) 0, null, "0"},
                    {" COMPARE %s %s %s ", (byte) -1, "Custom Error", "Custom Error"},
                    {" COMPARE %s %s %s ", (byte) -1, null, "1"},
            };
}

/// <summary>
/// Comparison expressions evaluation for the FieldIf and FieldCompare.
/// </summary>
private static class ComparisonExpressionEvaluator implements IComparisonExpressionEvaluator {
    public ComparisonExpressionEvaluator(ComparisonEvaluationResult result) {
        mResult = result;
    }

    public ComparisonEvaluationResult evaluate(Field field, ComparisonExpression expression) {
        mInvocations.add(new String[]
                {
                        expression.getLeftExpression(),
                        expression.getComparisonOperator(),
                        expression.getRightExpression()
                });

        return mResult;
    }

    public ComparisonExpressionEvaluator assertInvocationsCount(int expected) {
        Assert.assertEquals(expected, mInvocations.size());
        return this;
    }

    public ComparisonExpressionEvaluator assertInvocationArguments(
            int invocationIndex,
            String expectedLeftExpression,
            String expectedComparisonOperator,
            String expectedRightExpression) {
        String[] arguments = mInvocations.get(invocationIndex);

        Assert.assertEquals(expectedLeftExpression, arguments[0]);
        Assert.assertEquals(expectedComparisonOperator, arguments[1]);
        Assert.assertEquals(expectedRightExpression, arguments[2]);

        return this;
    }

    private final ComparisonEvaluationResult mResult;
    private final ArrayList<String[]> mInvocations = new ArrayList<>();
}