如何使用嵌套生成器编写jqwik生成器方法

vijay 发表于 Java

维杰：

使用jqwik.net，尝试生成其中包含嵌套RuleConfig类的Rule类。RuleConfig类具有一个嵌套的ruleProps，它是一个Map

statusReturnedFromApplyingRule方法始终返回初始化的规则，而不是使用@provide方法的值？返回的规则：rule:Rule{ruleId='null', inputMetricSelector=null, ruleConfig='RuleConfig{ruleType='null', ruleProps={}}'}, elements:[{}]

这是我的代码：

public class RangeMatchRuleTest {

    @Property
    @Report(Reporting.GENERATED)
    boolean statusReturnedFromApplyingRule(@ForAll("generateRule") Rule rule,
                                           @ForAll("generateInputMapElements") Iterable<Map<String, Object>> elements) {
        RangeMatchRule rangeMatchRule = new RangeMatchRule();
        final RuleIF.Status status = rangeMatchRule.applyRule(rule, elements);
        return RuleIF.getEnums().contains(status.toString());
    }

    @Provide
    Arbitrary<Rule> generateRule() {
        Rule rule = new Rule();
        RuleConfig ruleConfig = new RuleConfig();
        Map<String, Object> ruleProps = new HashMap<>();

        Arbitrary<Double> lowThresholdArb = Arbitraries.doubles()
                .between(0.0, 29.0);
        lowThresholdArb.allValues().ifPresent(doubleStream -> ruleProps.put(Utils.LOW_THRESHOLD, doubleStream.findFirst().get()));
        //lowThresholdArb.map(lowThreshold -> ruleProps.put(Utils.LOW_THRESHOLD, lowThreshold) );
        Arbitrary<Double> highThresholdArb = Arbitraries.doubles()
                .between(30.0, 50.0);
        highThresholdArb.map(highThreshold -> ruleProps.put(Utils.HIGH_THRESHOLD, highThreshold));
        ruleConfig.setRuleProps(ruleProps);
        rule.setRuleConfig(ruleConfig);
        return Arbitraries.create(() -> rule);
    }

    @Provide
    Arbitrary<Iterable<Map<String, Object>>> generateInputMapElements() {
        Arbitrary<Double> metricValueArb = Arbitraries.doubles()
                .between(0, 50.0);
        Map<String, Object> inputMap = new HashMap<>();
        metricValueArb.map(metricValue -> inputMap.put(Utils.METRIC_VALUE, metricValue));
        List<Map<String, Object>> inputMapLst = new ArrayList<>();
        inputMapLst.add(inputMap);
        return Arbitraries.create(() -> inputMapLst);
    }
}

TIA

johanneslink：

您generateRule在错误的假设上构建方法，即任意map方法在被调用时会执行任何实际操作。不是这种情况。map返回另一个任意实例的事实给出了强烈的暗示。

您必须掌握的基本思想是，提供者方法（带有方法注释@Provide）只是生成过程的“描述”而已。它只会被调用一次。实际对象的生成随后发生，并由框架控制。

这是经过改写的generateRule方法，应该可以实现您的预期目的：

@Provide
Arbitrary<Rule> generateRule() {
    Arbitrary<Double> lowThresholdArb = Arbitraries.doubles()
                                                   .between(0.0, 29.0);
    Arbitrary<Double> highThresholdArb = Arbitraries.doubles()
                                                    .between(30.0, 50.0);

    Arbitrary<RuleConfig> configArb =
        Combinators.combine(lowThresholdArb, highThresholdArb)
                   .as((low, high) -> {
                       Map<String, Object> ruleProps = new HashMap<>();
                       ruleProps.put(Utils.LOW_THRESHOLD, low);
                       ruleProps.put(Utils.HIGH_THRESHOLD, high);
                       RuleConfig ruleConfig = new RuleConfig();
                       ruleConfig.setRuleProps(ruleProps);
                       return ruleConfig;
                   });

    return configArb.map(config -> {
        Rule rule = new Rule();
        rule.setRuleConfig(config);
        return rule;
    });
}

您希望看到的是，创建生成器就像数据流编程一样：从一些基本的任意值开始- lowThresholdArb然后highThresholdArb-将它们组合，映射和过滤。最后，Arbitrary必须返回一个实例。

顺便说一句：如果希望每次需要使用此生成器时Rule，可以编写以下类：

public class RuleArbitraryProvider implements ArbitraryProvider {

    @Override
    public boolean canProvideFor(TypeUsage targetType) {
        return targetType.isOfType(Rule.class);
    }

    @Override
    public Set<Arbitrary<?>> provideFor(TypeUsage targetType, SubtypeProvider subtypeProvider) {
        return Collections.singleton(generateRule());
    }

    private Arbitrary<Rule> generateRule() {
        // Put here the code from above
        ...
    }
}

并将其注册为默认提供程序。

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