WIP: Fix test failures that occur with "nondex" plugin

[HildoYe]

This PR fixes several flaky tests:

1. There are several flaky tests in DynamicModelSerializationTest. The root cause of them is that equals() compares two HashMap<String, T> dynamicProperties in DynamicModel.
   In this PR, LinkedHashMap is used instead of HashMap to resolve the ordering issue. This solution considers 2 DynamicModels are same if their elements have the same insertion order. However, the equals() function should be modified to completely resolve the ordering issue.
2. There are several flaky tests in RequestBuilderTest. In these tests multiple pairs of JSON strings are compared with each other.
   In this PR, JSONAssert library is used to ignore the order difference when comparing 2 JSON strings.
3. There are a couple of flaky test in RequestUtilsTest. The root cause of them is the inconsistency when comparing 2 maps.
   In this PR, the comparations are changed to match the style of other tests in the same files while ignoring the ordering issue.

[CLAassistant]

All committers have signed the CLA.

[padamstx]

Hi @HildoYe, could you perhaps provide more info about the environment where you are seeing test failures occur?
Which OS are you using and which version of Java, for example?
That would help me understand a bit more about how/when these failures might occur.

On our team, we typically use either Mac or Linux for development work along with Java 8, and we have not seen these "flakey" test results in the past.

[HildoYe]

Hi @HildoYe, could you perhaps provide more info about the environment where you are seeing test failures occur? Which OS are you using and which version of Java, for example? That would help me understand a bit more about how/when these failures might occur.

On our team, we typically use either Mac or Linux for development work along with Java 8, and we have not seen these "flakey" test results in the past.

The tests I've done are in Linux and Java 8. It can be reproduced with mvn -pl . edu.illinois:nondex-maven-plugin:1.1.2:nondex -Dtest=TESTNAME
List:

DynamicModelSerializationTest#testAddlPropsNull DynamicModelSerializationTest#testAlternatePropertyNames DynamicModelSerializationTest#testDynamicModelMethods DynamicModelSerializationTest#testModelAPFoo DynamicModelSerializationTest#testModelAPFooNullTypeToken DynamicModelSerializationTest#testModelAPInteger DynamicModelSerializationTest#testModelAPObject DynamicModelSerializationTest#testModelAPProtectedCtor DynamicModelSerializationTest#testModelAPString DynamicModelSerializationTest#testNullValues RequestBuilderTest#testBodyContent1 RequestBuilderTest#testBodyContent3 RequestBuilderTest#testBodyContentList RequestUtilsTest#testOmitWithNulls RequestUtilsTest#testPickWithNulls 

[padamstx]

@HildoYe did you see the unit test failures only when using your edu.illinois:nondex-maven-plugin:1.1.2:nondex plugin?
The reason I ask is that we haven't seen any actual unit test failures on Mac or Linux.
Also a bit curious about the reason for your involvement here. Are you using an IBM Cloud SDK that depends on the java core library or are you simply experimenting with the java core to exercise your maven plugin?

Edit: I was able to run a couple of the tests with the "nondex" plugin and see the failures. Since these failures seem to occur only when the plugin is used, I think we'll hold off on merging in this PR for now. Thank you for bringing this to our attention though.

[padamstx]

closing without merging as we don't plan to merge this one in...