Add Unit test

log4j-api-test/src/test/java/org/apache/logging/log4j/spi/LoggerRegistryTest.java

@@ -0,0 +1,64 @@
+/*
+ * 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 org.apache.logging.log4j.spi;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.lang.ref.WeakReference;
+import java.util.stream.Stream;
+import org.apache.logging.log4j.message.MessageFactory;
+import org.apache.logging.log4j.message.ParameterizedMessageFactory;
+import org.apache.logging.log4j.message.ReusableMessageFactory;
+import org.apache.logging.log4j.test.TestLogger;
+import org.jspecify.annotations.Nullable;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.MethodSource;
+
+class LoggerRegistryTest {
+
+    private static final String LOGGER_NAME = LoggerRegistryTest.class.getName();
+
+    static Stream<@Nullable MessageFactory> doesNotLoseLoggerReferences() {
+        return Stream.of(
+                ParameterizedMessageFactory.INSTANCE,
+                ReusableMessageFactory.INSTANCE,
+                new ParameterizedMessageFactory(),
+                null);
+    }
+
+    /**
+     * @see <a href="https://github.com/apache/logging-log4j2/issues/3143>Issue #3143</a>
+     */
+    @ParameterizedTest
+    @MethodSource
+    void doesNotLoseLoggerReferences(@Nullable MessageFactory messageFactory) {
+        LoggerRegistry<TestLogger> loggerRegistry = new LoggerRegistry<>();
+        TestLogger logger = new TestLogger(LOGGER_NAME, messageFactory);
+        WeakReference<TestLogger> loggerRef = new WeakReference<>(logger);
+        // Register logger
+        loggerRegistry.putIfAbsent(LOGGER_NAME, messageFactory, logger);
+        // The JIT compiler/optimizer might figure out by himself the `logger` and `messageFactory` are no longer used:
+        //   https://shipilev.net/jvm/anatomy-quarks/8-local-var-reachability/
+        // We help him with the task though.
+        logger = null;
+        // Trigger a GC run
+        System.gc();
+        // Check if the logger is still there
+        assertThat(loggerRef.get()).isNotNull();
+        assertThat(loggerRegistry.getLogger(LOGGER_NAME, messageFactory)).isInstanceOf(TestLogger.class);
+    }
+}