[SCB-2718] Fix flaky test failure in TestOperationGenerator#apiOperationThenResponse

[MohsenDehghankar]

What is the purpose of this PR

• This PR fixes the flaky test org.apache.servicecomb.swagger.generator.core.TestOperationGenerator.apiOperationThenResponse
• The mentioned test may fail or pass without changes made to the source code when it is run in different JVMs due to the non-deterministic order of the returned array from getDeclaredAnnotations. Because there is no assumption on the order of the returned array from this method in Java documentation.

Why the test fails

• When processing the annotations of a method in AbstractOperationGenerator#scanMethodAnnotations(), the result of method.getAnnotations() is used which uses AccessibleObject.getDeclaredAnnotations() which does not guarantee a deterministic result order based on Java specifications.
• This results in processing annotations in arbitrary order, so the expected assertions in both TestOperationGenerator#apiOperationThenResponse and TestOperationGenerator#responseThenApiOperation might fail due to this change in orders of annotations.

Reproduce the test failure

• Run the test with 'NonDex' maven plugin. The command to recreate the flaky test failure is mvn edu.illinois:nondex-maven-plugin:2.1-SNAPSHOT:nondex -pl swagger/swagger-generator/generator-core -Dtest=TestOperationGenerator#apiOperationThenResponse
• Fixing the flaky test now may prevent flaky test failures in future Java versions.

Expected Result

• The tests should run successfully when run with 'NonDex' maven with the same command for recreating the flaky test.

Actual Result

• We get the following error:

[ERROR] Tests run: 1, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 0.258 s <<< FAILURE! - in org.apache.servicecomb.swagger.generator.core.TestOperationGenerator
[ERROR] org.apache.servicecomb.swagger.generator.core.TestOperationGenerator.apiOperationThenResponse  Time elapsed: 0.25 s  <<< FAILURE!
org.opentest4j.AssertionFailedError: expected: <null> but was: <io.swagger.models.properties.StringProperty@8f5d1e11>
        at org.junit.jupiter.api.AssertionFailureBuilder.build(AssertionFailureBuilder.java:151)
        at org.junit.jupiter.api.AssertionFailureBuilder.buildAndThrow(AssertionFailureBuilder.java:132)
        at org.junit.jupiter.api.AssertNull.failNotNull(AssertNull.java:50)
        at org.junit.jupiter.api.AssertNull.assertNull(AssertNull.java:35)
        at org.junit.jupiter.api.AssertNull.assertNull(AssertNull.java:30)
        at org.junit.jupiter.api.Assertions.assertNull(Assertions.java:276)
        at org.apache.servicecomb.swagger.generator.core.TestOperationGenerator.apiOperationThenResponse(TestOperationGenerator.java:114)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:566)
        at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
        at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
        at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
        at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
        at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
        at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
        at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
        at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
        at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
        at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
        at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
        at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
        at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
        at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
        at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
        at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
        at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
        at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
        at org.junit.runner.JUnitCore.run(JUnitCore.java:115)
        at org.junit.vintage.engine.execution.RunnerExecutor.execute(RunnerExecutor.java:42)
        at org.junit.vintage.engine.VintageTestEngine.executeAllChildren(VintageTestEngine.java:80)
        at org.junit.vintage.engine.VintageTestEngine.execute(VintageTestEngine.java:72)
        at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:147)
        at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:127)
        at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:90)
        at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:55)
        at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:102)
        at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:54)
        at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:114)
        at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:86)
        at org.junit.platform.launcher.core.DefaultLauncherSession$DelegatingLauncher.execute(DefaultLauncherSession.java:86)
        at org.apache.maven.surefire.junitplatform.LazyLauncher.execute(LazyLauncher.java:55)
        at org.apache.maven.surefire.junitplatform.JUnitPlatformProvider.execute(JUnitPlatformProvider.java:223)
        at org.apache.maven.surefire.junitplatform.JUnitPlatformProvider.invokeAllTests(JUnitPlatformProvider.java:175)
        at org.apache.maven.surefire.junitplatform.JUnitPlatformProvider.invoke(JUnitPlatformProvider.java:139)
        at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:456)
        at org.apache.maven.surefire.booter.ForkedBooter.execute(ForkedBooter.java:169)
        at org.apache.maven.surefire.booter.ForkedBooter.run(ForkedBooter.java:595)
        at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:581)

Fix

• First, we should sort the method.getAnnotations() result deterministically.
• Secondly, there should be no different in the assertEqual expressions between these two tests: apiOperationThenResponse and responseThenApiOperation

[liubao68]

Thanks for your PR.

[omkrpt]

This PR also fixes the flaky test org.apache.servicecomb.swagger.generator.core.TestOperationGenerator.responseThenApiOperation

To test this fix:
In swagger/swagger-generator/generator-core/pom.xml set parent artifact swagger-generator version from 2.9.0-SNAPSHOT to 2.8.1

Checkout the last commit before fix (5f02b0a33b51dcc93fe96c833311cc0fc8d444e7) and run the test with:
mvn edu.illinois:nondex-maven-plugin:2.1.1:nondex -pl swagger/swagger-generator/generator-core -Dtest=TestOperationGenerator#responseThenApiOperation

You will get failures.

Then checkout the commit with the fix (b780639a167ca09daaae28535c91c3b022f5d27c) and run the same. The test should no longer fail.