Fixed non-idempotent unit tests

[kaiyaok2]

Motivation:

The following tests are not idempotent and fail in repeated runs in the same environment, because it pollutes a state reused by itself:

• StateMachineUnNormalTest#testConditionNotMeet
• StateMachinePlantUMLTest#testPlantUML
• StateMachineChoiceTest#testChoice
• StateMachineTest#testMultiThread
• StateMachineTest#testParallel
• StateMachineTest#testExternalTransitionsNormal
• StateMachineTest#testExternalInternalNormal
• StateMachineTest#testInternalNormal
• StateMachineTest#testVerify
• StateMachineTest#testExternalNormal
• StateMachineTest#testFail

Take StateMachineUnNormalTest#testConditionNotMeet as an example: it constructs a state machine with a fixed ID "NotMeetConditionMachine". Then, in the second run, an error will be thrown since the state machine with ID "NotMeetConditionMachine" already exists. A fix is recommended since unit tests should be idempotent (deterministically passing in repeated runs).

Stacktrace of failure in the second run:

com.alibaba.cola.statemachine.impl.StateMachineException: The state machine with id [NotMeetConditionMachine] is already built, no need to build again
	at com.alibaba.cola.statemachine.StateMachineFactory.register(StateMachineFactory.java:20)
	at com.alibaba.cola.statemachine.builder.StateMachineBuilderImpl.build(StateMachineBuilderImpl.java:57)
	at com.alibaba.cola.test.StateMachineUnNormalTest.testConditionNotMeet(StateMachineUnNormalTest.java:32)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)

Reproduce:

Using the NIOInspector plugin that supports rerunning JUnit tests in the same environment. Use StateMachineTest#testMultiThread as an example:

cd cola-component-statemachine
mvn edu.illinois:NIOInspector:rerun -Dtest=com.alibaba.cola.test.StateMachineTest#testMultiThread

Proposed Fix

Assign a unique ID to each state machine used for testing.