Fix Flaky Test in JsonPOJOMapperTest

[cperkkk]

Fix Flaky Test in JsonPOJOMapperTest

Motivation

Problem

The testSerialization unit test in JsonPOJOMapperTest fails intermittently due to non-deterministic ordering of fields in the JSON output string. The test compares the exact string representation of a serialized JSON object.

The object also contains a HashMap<String, Object> field. Since HashMap does not guarantee iteration order, the serialized JSON string may have fields in different orders, causing the test to fail (even though the serialized data is semantically correct).

The fix ensures the test is robust to non-deterministic behaviors of java.util.Map and compatible with future updates to it or related dependencies. Let me know if further improvements or clarifications are needed!

Solution

The fix involves two changes to ensure consistent field ordering:

1. Add @JsonPropertyOrder annotation to the MyType class to enforce a specific order for top-level fields during serialization
2. Change HashMap to LinkedHashMap for the c field to preserve insertion order of nested map entries

@JsonPropertyOrder({"a", "b", "c", "d", "e"}) // changes here
public static class MyType {
  public int a;
  public String b;
  public HashMap<String, Object> c = new LinkedHashMap<>(); //changes here
  public List<MyType> d = new ArrayList<>();
  public List<Integer> e = new ArrayList<>();
}

Reproduction of Bug

Use the TestingResearchIllinois's NonDex tool and run:

mvn edu.illinois:nondex-maven-plugin:2.1.7:nondex -pl vertx-core -Dtest=JsonPOJOMapperTest

Error Message

Before the fix:

After the fix:

Conformance

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[cperkkk]

Hi @vietj seems like there's another flaky test unrelated to this that makes the check fails.

Please kindly advise on what to do, thank you!

[vietj]

@cperkkk can you rebase on latest ? this test has been rewritten recently

[cperkkk]

I have rebased the branch, thanks a lot @vietj

[cperkkk]

I have merged changes from main again since you fixed another flaky test as well @vietj