[Java] add test utils (#77)

add test utils

java/fury-core/src/test/java/io/fury/TestUtils.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2023 The Fury authors
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.fury;
+
+import com.google.common.collect.ImmutableBiMap;
+import com.google.common.collect.ImmutableMap;
+import io.fury.util.FieldAccessor;
+import io.fury.util.ReflectionUtils;
+import java.util.ArrayList;
+import java.util.function.Supplier;
+
+/**
+ * Test utils.
+ *
+ * @author chaokunyang
+ */
+public class TestUtils {
+  @SuppressWarnings("unchecked")
+  public static <T> T getFieldValue(Object obj, String fieldName) {
+    return (T)
+        FieldAccessor.createAccessor(ReflectionUtils.getField(obj.getClass(), fieldName)).get(obj);
+  }
+
+  public static <K, V> ImmutableMap<K, V> mapOf(K k1, V v1) {
+    return ImmutableBiMap.of(k1, v1);
+  }
+
+  /**
+   * Trigger OOM for SoftGC by allocate more memory.
+   *
+   * @param predicate whether stop Trigger OOM.
+   */
+  public static void triggerOOMForSoftGC(Supplier<Boolean> predicate) {
+    while (predicate.get()) {
+      // Force an OoM
+      try {
+        final ArrayList<Object[]> allocations = new ArrayList<>();
+        int size;
+        while ((size =
+                Math.min(Math.abs((int) Runtime.getRuntime().freeMemory()), Integer.MAX_VALUE))
+            > 0) allocations.add(new Object[size]);
+      } catch (OutOfMemoryError e) {
+        System.out.println("Trigger OOM to clear LoaderBinding.furySoftMap soft references.");
+      }
+      System.gc();
+      try {
+        Thread.sleep(1000);
+      } catch (InterruptedException e) {
+        throw new RuntimeException(e);
+      }
+      System.out.printf("Wait gc.");
+    }
+  }
+}