Fix Java 11+ compatibility and add unit tests

pom.xml

@@ -39,10 +39,21 @@
             <version>${json.version}</version>
             <scope>provided</scope>
         </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <version>5.10.2</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>
         <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>3.2.5</version>
+            </plugin>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-install-plugin</artifactId>

src/main/java/org/apache/tomcat/cloud/KubernetesMemberProvider.java

@@ -26,7 +26,6 @@
 import org.json.JSONException;
 import org.json.JSONObject;
 import org.json.JSONTokener;
-import sun.reflect.generics.reflectiveObjects.NotImplementedException;
 
 import java.io.IOException;
 import java.io.InputStream;
@@ -96,7 +95,7 @@ public void init(Properties properties) throws IOException {
             streamProvider = new TokenStreamProvider(saToken, caCertFile);
         } else {
             // TODO: implement CertificateStreamProvider
-            throw new NotImplementedException();
+            throw new UnsupportedOperationException("CertificateStreamProvider is not yet implemented");
         }
 
         String ver = getEnv(ENV_PREFIX + "API_VERSION");

src/test/java/org/apache/tomcat/cloud/AbstractMemberProviderTest.java

@@ -0,0 +1,119 @@
+/*
+ * 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.tomcat.cloud;
+
+import org.apache.catalina.tribes.Member;
+import org.junit.jupiter.api.Assumptions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Properties;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class AbstractMemberProviderTest {
+
+    private ConcreteProvider provider;
+
+    @BeforeEach
+    void setUp() {
+        provider = new ConcreteProvider();
+    }
+
+    // -------------------------------------------------------------------------
+    // constructor
+    // -------------------------------------------------------------------------
+
+    @Test
+    void constructor_initializesMd5() {
+        // MD5 is guaranteed by the Java Security specification on all compliant JVMs.
+        // If the algorithm were unavailable the field would silently remain null, which
+        // would cause a NullPointerException the first time digest() is called in a subclass.
+        assertNotNull(provider.md5, "md5 digest should be initialized in constructor");
+    }
+
+    // -------------------------------------------------------------------------
+    // getEnv()
+    // -------------------------------------------------------------------------
+
+    @Test
+    void getEnv_returnsNullWhenKeyNotFound() {
+        assertNull(provider.getEnvForTest("THIS_ENV_KEY_DOES_NOT_EXIST_12345"));
+    }
+
+    @Test
+    void getEnv_returnsNullWhenAllKeysMissing() {
+        assertNull(provider.getEnvForTest("FAKE_KEY_AAA_99999", "FAKE_KEY_BBB_99999"));
+    }
+
+    @Test
+    void getEnv_noKeys_returnsNull() {
+        // Calling getEnv() with an empty varargs array must return null because the loop
+        // body never executes.
+        assertNull(provider.getEnvForTest());
+    }
+
+    @Test
+    void getEnv_nullKey_throwsNullPointerException() {
+        // System.getenv(null) throws NullPointerException per the Java specification.
+        // A null element in the keys array propagates that exception to the caller.
+        // This documents that null keys are not supported; callers must ensure all keys
+        // are non-null.
+        assertThrows(NullPointerException.class,
+                () -> provider.getEnvForTest((String) null));
+    }
+
+    @Test
+    void getEnv_returnsFirstNonNullValue() {
+        String pathValue = System.getenv("PATH");
+        Assumptions.assumeTrue(pathValue != null, "PATH env var not available, skipping");
+
+        String result = provider.getEnvForTest("THIS_KEY_DOES_NOT_EXIST", "PATH");
+        assertEquals(pathValue, result, "Should skip missing keys and return the first found value");
+    }
+
+    @Test
+    void getEnv_stopsAtFirstFoundKey() {
+        String pathValue = System.getenv("PATH");
+        Assumptions.assumeTrue(pathValue != null, "PATH env var not available, skipping");
+
+        String result = provider.getEnvForTest("PATH", "THIS_KEY_DOES_NOT_EXIST");
+        assertEquals(pathValue, result, "Should return immediately when the first key is found");
+    }
+
+    // -------------------------------------------------------------------------
+    // Helper: concrete subclass to expose protected members for testing
+    // -------------------------------------------------------------------------
+
+    private static class ConcreteProvider extends AbstractMemberProvider {
+
+        String getEnvForTest(String... keys) {
+            return getEnv(keys);
+        }
+
+        @Override
+        public void init(Properties properties) throws Exception {}
+
+        @Override
+        public List<? extends Member> getMembers() throws Exception {
+            return Collections.emptyList();
+        }
+    }
+}