[#4966] Fixing flaky test UnitTestSwaggerUtils#testSwagger without adding dependencies

[pem70]

Issue

The method testSwagger () in UnitTestSwaggerUtils from module swagger/swagger-generator/generator-core compares pretty-printed YAML strings to verify correctness. However, since the OpenAPI object is constructed with Map/Set iteration, the key order in the serialized YAML is non-deterministic. When the iteration order changes, the string comparison fails, resulting in flaky behavior.

This test was flagged by the NonDex tool, which detects unreliable tests caused by hidden assumptions in Java API ordering. To reproduce, run an upper test that calls testSwagger, for example:

mvn -pl swagger/swagger-generator/generator-core   edu.illinois:nondex-maven-plugin:2.1.7:nondex   -Dtest=org.apache.servicecomb.swagger.generator.core.TestSwaggerUtils#testSchemaMethod

Affected Tests

This change fixes the below tests:
org.apache.servicecomb.swagger.generator.core.TestPojo.testResponseEntity
org.apache.servicecomb.swagger.generator.core.TestSwaggerUtils.testSchemaMethod
org.apache.servicecomb.swagger.generator.core.TestPojoExample.testPojoExample1

Fix

Instead of comparing raw YAML strings or using JSONAssert as my previous PR, the new implementation parses both expected and actual OpenAPI YAML into JsonNode objects using Jackson’s ObjectMapper and YAMLFactory.
It then checks structural equality via JsonNode.equals(), ensuring order-insensitive comparison while preserving strict value matching.

Rerunning NonDex with this change shows a stable passing result.

PR Checklist

• Github Issue: [BUG] - Flaky test in UnitTestSwaggerUtils#testSwagger (#4966 )
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