fix(java): Fix flakiness in ExpressionVisitorTest#testTraverseExpress…

…ion (#1968)

## What does this PR do?

`ExpressionVisitorTest#testTraverseExpression` relies on ordered
traversal. However, the traversal depends on the order of
`getDeclaredFields()` to be deterministic (see below). The Java
specification explicitly marks `getDeclaredFields` as a function that
can return field names in any order. In the wild, this is most likely to
manifest on different architectures with different JVM versions.


https://github.com/apache/fury/blob/54b62fb6ab5d7e557131efe07c7402c885f6e7c4/java/fury-core/src/main/java/org/apache/fury/reflect/ReflectionUtils.java#L368-L381

Using [NonDex](https://github.com/TestingResearchIllinois/NonDex), we
can replicate the flaky behavior with the following command:

```
mvn edu.illinois:nondex-maven-plugin:2.1.7:nondex -pl fury-core/ -Dcheckstyle.skip -Dmaven.javadoc.skip -Dtest=org.apache.fury.codegen.ExpressionVisitorTest
```

The fix, in this case, is to simply use HashSet equality instead of an
ordered List equality. The above NonDex command should succeed after
applying this patch.

I do, however, note that there are other flaky tests (found by running
NonDex on the entire `fury-core` project) that fail due to reliance on
e.g. `PriorityQueue#toArray`, which is also explicity marked to return
nondeterministically ordered arrays.

## Does this PR introduce any user-facing change?

No

---------

Co-authored-by: Shawn Yang <[email protected]>

java/fury-core/src/test/java/org/apache/fury/codegen/ExpressionVisitorTest.java

@@ -26,7 +26,9 @@
 import java.lang.reflect.Method;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 import org.apache.fury.codegen.Expression.Literal;
 import org.apache.fury.reflect.ReflectionUtils;
 import org.apache.fury.reflect.TypeRef;
@@ -63,7 +65,11 @@ public void testTraverseExpression() throws InvocationTargetException, IllegalAc
     assertEquals(serializedLambda.getCapturedArgCount(), 1);
     ExpressionVisitor.ExprHolder exprHolder =
         (ExpressionVisitor.ExprHolder) (serializedLambda.getCapturedArg(0));
-    assertEquals(
-        expressions, Arrays.asList(forLoop, start, end, step, e1, ref, exprHolder.get("e2")));
+
+    // Traversal relies on getDeclaredFields(), nondeterministic order.
+    Set<Expression> expressionsSet = new HashSet<>(expressions);
+    Set<Expression> expressionsSet2 =
+        new HashSet<>(Arrays.asList(forLoop, e1, ref, exprHolder.get("e2"), end, start, step));
+    assertEquals(expressionsSet, expressionsSet2);
   }
 }