Fix flaky test in CustomTypeAdaptersTest

[219sansim]

Purpose

The test testCustomNestedSerializers in CustomTypeAdaptersTest is detected flaky because the gson.toJson() gives a non-deterministic output.
Related issue: #2520

Description

After modifying the tests to check if the gson.toJson() output to is one of the possible json string values, the test passes, instead of checking against only 1 string.

Reason:
The gson.toJson() internally calls com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields which makes a call to getDeclaredFields

gson/gson/src/main/java/com/google/gson/internal/bind/ReflectiveTypeAdapterFactory.java

Line 265 in e685705

Field[] fields = raw.getDeclaredFields();

And according to this stackoverlow discussion, getDeclaredFields in Java 8 does not return elements in a consistent order.

Reproduction of error

The test runs fail on 4/5 runs of the NonDex tool

Command to reproduce the failure:

mvn -pl gson edu.illinois:nondex-maven-plugin:2.1.1:debug -Dtest=com.google.gson.functional.CustomTypeAdaptersTest#testCustomNestedSerializers

Error Message:

Running com.google.gson.functional.CustomTypeAdaptersTest
[ERROR] Tests run: 1, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 0.689 s <<< FAILURE! -- in com.google.gson.functional.CustomTypeAdaptersTest
[ERROR] com.google.gson.functional.CustomTypeAdaptersTest.testCustomNestedSerializers -- Time elapsed: 0.660 s <<< FAILURE!
value of: toJson(...)
expected: {"bag":6,"value":10}
but was : {"value":10,"bag":6}
        at com.google.gson.functional.CustomTypeAdaptersTest.testCustomNestedSerializers(CustomTypeAdaptersTest.java:128)

[INFO] 
[INFO] Results:
[INFO] 
[ERROR] Failures: 
[ERROR]   CustomTypeAdaptersTest.testCustomNestedSerializers:128 value of: toJson(...)
expected: {"bag":6,"value":10}
but was : {"value":10,"bag":6}
[INFO] 
[ERROR] Tests run: 1, Failures: 1, Errors: 0, Skipped: 0
[INFO] 

[MaicolAntali]

Here, instead of using .equals()s, you can you the .isAnyOf(obj1, obj2) method.
According with the .isAnyOf() documentation:

Fails unless the subject is equal to any of the given elements.

The assert could be something like:

Suggested change

	String targetStr = gson.toJson(target);
	assertThat(targetStr.equals("{\"bag\":6,\"value\":10}") || targetStr.equals("{\"value\":10,\"bag\":6}")).isTrue();
	assertThat(gson.toJson(target)).isAnyOf("{\"bag\":6,\"value\":10}", "{\"value\":10,\"bag\":6}");

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Note: I am not a maintainer of the project, please wait for a maintainer's review