Added unit tests for RefCountedReleasable

Signed-off-by: Kartik Ganesh <[email protected]>

server/src/test/java/org/opensearch/common/concurrent/RefCountedReleasableTests.java

@@ -0,0 +1,68 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+/*
+ * Modifications Copyright OpenSearch Contributors. See
+ * GitHub history for details.
+ */
+
+package org.opensearch.common.concurrent;
+
+import org.junit.Before;
+import org.opensearch.test.OpenSearchTestCase;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class RefCountedReleasableTests extends OpenSearchTestCase {
+
+    private AtomicInteger testRef;
+    private RefCountedReleasable<AtomicInteger> testObject;
+
+    @Before
+    public void setup() {
+        testRef = new AtomicInteger(0);
+        testObject = new RefCountedReleasable<>("test", testRef, testRef::incrementAndGet);
+    }
+
+    public void testInitialState() {
+        assertEquals("test", testObject.getName());
+        assertEquals(testRef, testObject.get());
+        assertEquals(testRef, testObject.get());
+        assertEquals(0, testObject.get().get());
+        assertEquals(1, testObject.refCount());
+    }
+
+    public void testIncRef() {
+        testObject.incRef();
+        assertEquals(2, testObject.refCount());
+        assertEquals(0, testObject.get().get());
+    }
+
+    public void testCloseWithoutInternal() {
+        testObject.incRef();
+        assertEquals(2, testObject.refCount());
+        testObject.close();
+        assertEquals(1, testObject.refCount());
+        assertEquals(0, testObject.get().get());
+    }
+
+    public void testCloseWithInternal() {
+        assertEquals(1, testObject.refCount());
+        testObject.close();
+        assertEquals(0, testObject.refCount());
+        assertEquals(1, testObject.get().get());
+    }
+
+    public void testIncRefAfterClose() {
+        assertEquals(1, testObject.refCount());
+        testObject.close();
+        assertEquals(0, testObject.refCount());
+        assertEquals(1, testObject.get().get());
+        assertThrows(IllegalStateException.class, () -> testObject.incRef());
+    }
+}