org.powermock.reflect.exceptions.TooManyConstructorsFoundException: Several matching constructors found

Question

I have written sample Kafka Producer class, I tested this class with local configurations, its working fine. Now along with it I am trying to write corresponding test class, for that I am using concept of mockings concepts but getting some errors

My original class:-

public class SimpleProducer {

    private static final Logger logger = LogManager.getLogger(SimpleProducer.class);
    public static String message = null;
    public static void main(String[] args) throws Exception {

        String topicName = null;
        if(args.length == 0){
            logger.info("Run class by providing topic-name java -cp /path-of-the-jar/kafka-consumer-producer-jar-with-dependencies.jar com.ewt.SimpleProducer <topic-name> > kafka-consumer.log 2>&1 &");
            return;
        }
        else{
            topicName = args[0];
        }

        // create instance for properties to access producer configs
        Properties props = new Properties();

        // Assign localhost id
        props.put("bootstrap.servers", "localhost:9092");

        // Set acknowledgements for producer requests.
        props.put("acks", "all");

        // If the request fails, the producer can automatically retry,
        props.put("retries", 0);

        // Specify buffer size in config
        props.put("batch.size", 16384);

        // Reduce the no of requests less than 0
        props.put("linger.ms", 1);

        // The buffer.memory controls the total amount of memory available to
        // the producer for buffering.
        props.put("buffer.memory", 33554432);

        props.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer");

        props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");

        Producer<String, String> producer = new KafkaProducer<String, String>(props);

        for (int i = 0; i < 10; i++)
            producer.send(new ProducerRecord<String, String>(topicName, Integer.toString(i), Integer.toString(i)));
        message = "Messages sent successfully";
        logger.info(message);
        producer.close();
    }
}

Test Class:-

import java.util.Properties;

import org.apache.kafka.clients.producer.KafkaProducer;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mockito;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

import com.ewt.SimpleProducer;

@RunWith(PowerMockRunner.class)
@PrepareForTest(Properties.class)
public class SimpleProducerTest {

@Test
public void mainTest() throws Exception{
    Properties props = new Properties();
    KafkaProducer kafkaProducer = Mockito.mock(KafkaProducer.class);
        PowerMockito.whenNew(Properties.class).withNoArguments().thenReturn(props);
        PowerMockito.whenNew(KafkaProducer.class).withArguments(Properties.class).thenReturn(kafkaProducer); // showing error here
        //PowerMockito.whenNew(KafkaProducer.class).withArguments(props).thenReturn(kafkaProducer);//tried this one also, it is also giving same error
        Mockito.doNothing().when(kafkaProducer.send(Mockito.anyObject()));
        //Mockito.doNothing().when(kafkaProducer.close());
        String args[] = {"test-topic"};
        SimpleProducer.main(args);
        System.out.println(SimpleProducer.message);
    }
}

Getting the following error

org.powermock.reflect.exceptions.TooManyConstructorsFoundException: Several             
matching constructors found, please specify the argument parameter types so that PowerMock can determine which method you're referring to.
Matching constructors in class         org.apache.kafka.clients.producer.KafkaProducer were:
org.apache.kafka.clients.producer.KafkaProducer( java.util.Properties.class )
org.apache.kafka.clients.producer.KafkaProducer( java.util.Map.class )

at org.powermock.reflect.internal.WhiteboxImpl.throwExceptionWhenMultipleConstructorMatchesFound(WhiteboxImpl.java:1751)
at org.powermock.reflect.internal.WhiteboxImpl.findUniqueConstructorOrThrowException(WhiteboxImpl.java:1098)
at org.powermock.api.mockito.internal.expectation.DefaultConstructorExpectationSetup.createNewSubstituteMock(DefaultConstructorExpectationSetup.java:98)
at org.powermock.api.mockito.internal.expectation.DefaultConstructorExpectationSetup.withArguments(DefaultConstructorExpectationSetup.java:55)
at com.ewt.test.SimpleProducerTest.mainTest(SimpleProducerTest.java:24)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.internal.runners.TestMethod.invoke(TestMethod.java:68)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:326)
at org.junit.internal.runners.MethodRoadie$2.run(MethodRoadie.java:88)
at org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:96)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.executeTest(PowerMockJUnit44RunnerDelegateImpl.java:310)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTestInSuper(PowerMockJUnit47RunnerDelegateImpl.java:131)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.access$100(PowerMockJUnit47RunnerDelegateImpl.java:59)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner$TestExecutorStatement.evaluate(PowerMockJUnit47RunnerDelegateImpl.java:147)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.evaluateStatement(PowerMockJUnit47RunnerDelegateImpl.java:107)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTest(PowerMockJUnit47RunnerDelegateImpl.java:82)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runBeforesThenTestThenAfters(PowerMockJUnit44RunnerDelegateImpl.java:298)
at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:86)
at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:49)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.invokeTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:218)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.runMethods(PowerMockJUnit44RunnerDelegateImpl.java:160)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$1.run(PowerMockJUnit44RunnerDelegateImpl.java:134)
at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:33)
at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:45)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.run(PowerMockJUnit44RunnerDelegateImpl.java:136)
at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.run(JUnit4TestSuiteChunkerImpl.java:117)
at org.powermock.modules.junit4.common.internal.impl.AbstractCommonPowerMockRunner.run(AbstractCommonPowerMockRunner.java:57)
at org.powermock.modules.junit4.PowerMockRunner.run(PowerMockRunner.java:59)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

Answer 1

java.util.Properties is a java.util.Map so PowerMock is unable to distinguish between these two contructors:

org.apache.kafka.clients.producer.KafkaProducer( java.util.Properties.class )

org.apache.kafka.clients.producer.KafkaProducer( java.util.Map.class )

You can use withParameterTypes alongside withArguments to tell PowerMock exactly which contructor you are targetting.

For example:

PowerMockito.whenNew(KafkaProducer.class)
    .withParameterTypes(Properties.class)
    .withArguments(Properties.class)
    .thenReturn(kafkaProducer);